perf(messages): mechanical interpolation cleanups (#2436)

## Summary

Phase 3.1 of the message-interpolation optimization series. Fixes 9 of the 28 sites flagged in the Phase 2 audit (PR #2435):

| File | Fix |
|---|---|
| `Commands/StaffAccess.cs:88,99` | Drop redundant `.ToString()` on enum holes |
| `Commands/Handlers.cs:102` | `builder.ToString()` -> `builder.AsSpan()` |
| `World Saves/SaveCommands.cs:71-75` | Merge 3 concatenated `$"..."` into one literal |
| `Server/Items/Item.cs:4213` | Hoist nested ternary `$"..."` to if/else |
| `Engines/Factions/Mobiles/Guards/BaseFactionGuard.cs:140-150` | Convert switch expression to switch statement |
| `Mobiles/Monsters/LBR/Jukas/JukaLord.cs:85` | Restructure `string.Format(toSay.RandomElement(), ...)` into switch |
| `Misc/AttackMessage.cs:30-41` | Inline `AggressorFormat`/`AggressedFormat` constants |

No functional changes. Each site emits identical text; the only difference is that the message string is now built into a pooled char buffer instead of being allocated as a `string` first.

Projects/Server/Items/Item.cs

@@ -4106,6 +4106,20 @@ public partial class Item : IHued, IComparable<Item>, ISpawnable, IObjectPropert
                 );
             }
         }
+        else if (m_Amount > 1)
+        {
+            ns.SendMessage(
+                Serial,
+                m_ItemID,
+                MessageType.Label,
+                0x3B2,
+                3,
+                false,
+                "ENU",
+                "",
+                $"{Name} : {m_Amount}"
+            );
+        }
         else
         {
             ns.SendMessage(
@@ -4117,7 +4131,7 @@ public partial class Item : IHued, IComparable<Item>, ISpawnable, IObjectPropert
                 false,
                 "ENU",
                 "",
-                $"{Name}{(m_Amount > 1 ? $" : {m_Amount}" : "")}"
+                $"{Name}"
             );
         }
     }