fix: Optimizes OPL using string interpolation (#1041)

## Breaking Changes (New API)
ObjectPropertyList supports the following API:
```cs
list.Add(500000);
list.Add(500001, stringArgument);
list.Add("Some text");
list.Add($"Some text with {argument}");
list.Add(500002, $"{arg1}\t{arg2}");
```

## Notes
1. All API uses that require a formatter like this:
    ```cs
    list.Add(500002, "{0}\t{1}", arg1, arg2);
    ```
    Should be changed to use string interpolation, for example:
    ```cs
    list.Add(500002, $"{arg1}\t{arg2}");
    ```
2. The following paradigm should no longer be used:
    ```cs
    list.Add(1061170, prop.ToString()); // strength requirement ~1_val~
    ```
    The new string interpolation API will avoid having to convert the argument to a string before writing it to the packet. Instead use the following:
    ```cs
    list.Add(1061170, $"{prop}"); // strength requirement ~1_val~
    ```

### Benchmarks
```cs
|                         Method |     Mean |   Error |  StdDev |  Gen 0 | Allocated |
|------------------------------- |---------:|--------:|--------:|-------:|----------:|
|                BenchmarkOldOPL | 241.0 ns | 0.56 ns | 0.47 ns | 0.0105 |      88 B |
| BenchmarkStringInterpolatedOPL | 199.9 ns | 2.44 ns | 2.39 ns |      - |         - |
```

### Changes
- [X] Removes crash in STArray.Return when array is null.
- [X] Fixes NPE in OPL when entity is null. Serial in packet will be 0 when entity is null.
- [X] Fixes NPE in AosAttributes when Parent is null.
- [X] Changes OPL to use string interpolation.
- [X] Introduces `IPropertyList` to allow extending PropertyList for other uses.

Projects/UOContent/Items/Skill Items/Magical/Spellbook.cs

@@ -695,7 +695,7 @@ namespace Server.Items
             to.NetState.SendSpellbookContent(Serial, ItemID, BookOffset + 1, m_Content);
         }
 
-        public override void GetProperties(ObjectPropertyList list)
+        public override void GetProperties(IPropertyList list)
         {
             base.GetProperties(list);
 
@@ -738,72 +738,72 @@ namespace Server.Items
 
             if ((prop = Attributes.WeaponDamage) != 0)
             {
-                list.Add(1060401, prop.ToString()); // damage increase ~1_val~%
+                list.Add(1060401, $"{prop}"); // damage increase ~1_val~%
             }
 
             if ((prop = Attributes.DefendChance) != 0)
             {
-                list.Add(1060408, prop.ToString()); // defense chance increase ~1_val~%
+                list.Add(1060408, $"{prop}"); // defense chance increase ~1_val~%
             }
 
             if ((prop = Attributes.BonusDex) != 0)
             {
-                list.Add(1060409, prop.ToString()); // dexterity bonus ~1_val~
+                list.Add(1060409, $"{prop}"); // dexterity bonus ~1_val~
             }
 
             if ((prop = Attributes.EnhancePotions) != 0)
             {
-                list.Add(1060411, prop.ToString()); // enhance potions ~1_val~%
+                list.Add(1060411, $"{prop}"); // enhance potions ~1_val~%
             }
 
             if ((prop = Attributes.CastRecovery) != 0)
             {
-                list.Add(1060412, prop.ToString()); // faster cast recovery ~1_val~
+                list.Add(1060412, $"{prop}"); // faster cast recovery ~1_val~
             }
 
             if ((prop = Attributes.CastSpeed) != 0)
             {
-                list.Add(1060413, prop.ToString()); // faster casting ~1_val~
+                list.Add(1060413, $"{prop}"); // faster casting ~1_val~
             }
 
             if ((prop = Attributes.AttackChance) != 0)
             {
-                list.Add(1060415, prop.ToString()); // hit chance increase ~1_val~%
+                list.Add(1060415, $"{prop}"); // hit chance increase ~1_val~%
             }
 
             if ((prop = Attributes.BonusHits) != 0)
             {
-                list.Add(1060431, prop.ToString()); // hit point increase ~1_val~
+                list.Add(1060431, $"{prop}"); // hit point increase ~1_val~
             }
 
             if ((prop = Attributes.BonusInt) != 0)
             {
-                list.Add(1060432, prop.ToString()); // intelligence bonus ~1_val~
+                list.Add(1060432, $"{prop}"); // intelligence bonus ~1_val~
             }
 
             if ((prop = Attributes.LowerManaCost) != 0)
             {
-                list.Add(1060433, prop.ToString()); // lower mana cost ~1_val~%
+                list.Add(1060433, $"{prop}"); // lower mana cost ~1_val~%
             }
 
             if ((prop = Attributes.LowerRegCost) != 0)
             {
-                list.Add(1060434, prop.ToString()); // lower reagent cost ~1_val~%
+                list.Add(1060434, $"{prop}"); // lower reagent cost ~1_val~%
             }
 
             if ((prop = Attributes.Luck) != 0)
             {
-                list.Add(1060436, prop.ToString()); // luck ~1_val~
+                list.Add(1060436, $"{prop}"); // luck ~1_val~
             }
 
             if ((prop = Attributes.BonusMana) != 0)
             {
-                list.Add(1060439, prop.ToString()); // mana increase ~1_val~
+                list.Add(1060439, $"{prop}"); // mana increase ~1_val~
             }
 
             if ((prop = Attributes.RegenMana) != 0)
             {
-                list.Add(1060440, prop.ToString()); // mana regeneration ~1_val~
+                list.Add(1060440, $"{prop}"); // mana regeneration ~1_val~
             }
 
             if (Attributes.NightSight != 0)
@@ -813,17 +813,17 @@ namespace Server.Items
 
             if ((prop = Attributes.ReflectPhysical) != 0)
             {
-                list.Add(1060442, prop.ToString()); // reflect physical damage ~1_val~%
+                list.Add(1060442, $"{prop}"); // reflect physical damage ~1_val~%
             }
 
             if ((prop = Attributes.RegenStam) != 0)
             {
-                list.Add(1060443, prop.ToString()); // stamina regeneration ~1_val~
+                list.Add(1060443, $"{prop}"); // stamina regeneration ~1_val~
             }
 
             if ((prop = Attributes.RegenHits) != 0)
             {
-                list.Add(1060444, prop.ToString()); // hit point regeneration ~1_val~
+                list.Add(1060444, $"{prop}"); // hit point regeneration ~1_val~
             }
 
             if (Attributes.SpellChanneling != 0)
@@ -833,30 +833,30 @@ namespace Server.Items
 
             if ((prop = Attributes.SpellDamage) != 0)
             {
-                list.Add(1060483, prop.ToString()); // spell damage increase ~1_val~%
+                list.Add(1060483, $"{prop}"); // spell damage increase ~1_val~%
             }
 
             if ((prop = Attributes.BonusStam) != 0)
             {
-                list.Add(1060484, prop.ToString()); // stamina increase ~1_val~
+                list.Add(1060484, $"{prop}"); // stamina increase ~1_val~
             }
 
             if ((prop = Attributes.BonusStr) != 0)
             {
-                list.Add(1060485, prop.ToString()); // strength bonus ~1_val~
+                list.Add(1060485, $"{prop}"); // strength bonus ~1_val~
             }
 
             if ((prop = Attributes.WeaponSpeed) != 0)
             {
-                list.Add(1060486, prop.ToString()); // swing speed increase ~1_val~%
+                list.Add(1060486, $"{prop}"); // swing speed increase ~1_val~%
             }
 
             if (Core.ML && (prop = Attributes.IncreasedKarmaLoss) != 0)
             {
-                list.Add(1075210, prop.ToString()); // Increased Karma Loss ~1val~%
+                list.Add(1075210, $"{prop}"); // Increased Karma Loss ~1val~%
             }
 
-            list.Add(1042886, SpellCount.ToString()); // ~1_NUMBERS_OF_SPELLS~ Spells
+            list.Add(1042886, $"{SpellCount}"); // ~1_NUMBERS_OF_SPELLS~ Spells
         }
 
         public override void OnSingleClick(Mobile from)