fix: monster ability queries no longer have side effects (#2716)

## Problem
`GetMonsterAbilities()` answers three questions through one virtual: which abilities a creature has (`GetAbility`, `AOS.cs` reflect/barrier, bard fire-breath difficulty), which abilities are enabled right now, and where cooldown state must be cleaned up (`InvalidateNextAbilityTriggers` on death and delete). Every caller assumes it is a pure, stable list. About 70 creatures return a static array; only LordOaks computed it:

```
Mobile.Delete()
 → BaseCreature.OnDelete() → CreatureDeletedEvent
 → MonsterAbility.InvalidateNextAbilityTriggers()
 → LordOaks.GetMonsterAbilities() → CheckQueen() → new Silvani().MoveToWorld(...)
```

- Deleting a Lord Oaks nobody had fought (champion reset, `DeleteCreatures`, GM delete) spawned an orphaned Silvani where he stood.
- The spell damage scalar (`AlterDamageScalarFrom`) spawned her too.
- With the queen dead his list was empty, so cleanup skipped his cooldown entries. The static `Dictionary<BaseCreature, long>` on the ability singleton kept a reference to the deleted creature. `MonsterAbilityGroup` children's entries were never cleaned either.
- Neira threw unholy bones from `AlterDamageScalarFrom`, so any caller asking for a damage scalar (a preview gump, for example) could fire the effect.

## Changes
- **Per-creature cooldowns:** a lazy `Dictionary<MonsterAbility, long>` on `BaseCreature` (`IsAbilityOnCooldown`, `SetAbilityCooldown`, `ClearAbilityCooldowns`). The static dictionaries and the query-driven cleanup are gone, and death still resets cooldowns. Tick comparisons are wraparound-safe.
- **Pure contract:** `GetMonsterAbilities()` is documented as pure. The new `virtual bool CanUseAbility(MonsterAbility)` gates abilities that only work some of the time. Every `TriggerAbility*` loop and `GetAbility` check it.
- **LordOaks:** always lists his abilities; `CanUseAbility` and the 10% spell shield read "queen alive". The queen spawns when he is first aggressed or first given a combatant, never on the internal map. Aggression lands before the damage it causes, so the first spell is still shielded, as before.
- **Neira:** the unholy bone throw moves to `OnDamagedBySpell`.

A follow-up PR makes minions such as the queen, pixies and Barracoon's rats belong to their champion spawn, so a spawn reset cleans them up.

## Testing
- `LordOaksTests` covers three cases:
  - querying or deleting an unengaged Lord Oaks spawns nothing;
  - aggression spawns the queen exactly once, and the shield and abilities follow her life;
  - an Oaks on the internal map never spawns her.
- UOContent.Tests: 1234 passed, 2 skipped.
- A local constructor sweep (every Mobile built and deleted repeatedly) no longer reports LordOaks.

Projects/UOContent/Mobiles/Special/LordOaks.cs

@@ -86,7 +86,11 @@ public partial class LordOaks : BaseChampion
     public override Poison PoisonImmune => Poison.Deadly;
 
     private static MonsterAbility[] _abilities = { MonsterAbilities.SummonPixiesCounter };
-    public override MonsterAbility[] GetMonsterAbilities() => CheckQueen() ? _abilities : MonsterAbilities.Empty;
+    public override MonsterAbility[] GetMonsterAbilities() => _abilities;
+
+    public override bool CanUseAbility(MonsterAbility ability) => IsQueenAlive;
+
+    private bool IsQueenAlive => _queen?.Deleted == false;
 
     public override void GenerateLoot()
     {
@@ -103,36 +107,41 @@ public partial class LordOaks : BaseChampion
 
     public override int GetDeathSound() => 0x2F7;
 
-    public bool CheckQueen()
+    // Aggression lands before the damage it causes, so the queen is up before the first hit is scaled.
+    public override void AggressiveAction(Mobile aggressor, bool criminal)
     {
-        if (Map == null)
+        base.AggressiveAction(aggressor, criminal);
+        SpawnQueen();
+    }
+
+    public override void OnCombatantChange()
+    {
+        base.OnCombatantChange();
+
+        if (Combatant != null)
         {
-            return false;
+            SpawnQueen();
+        }
+    }
+
+    private void SpawnQueen()
+    {
+        if (_spawnedQueen || Deleted || Map == null || Map == Map.Internal)
+        {
+            return;
         }
 
-        if (!_spawnedQueen)
-        {
-            Say(1042153); // Come forth my queen!
+        Say(1042153); // Come forth my queen!
 
-            _queen = new Silvani { Team = Team };
-            _queen.MoveToWorld(Location, Map);
+        Queen = new Silvani { Team = Team };
+        Queen.MoveToWorld(Location, Map);
 
-            _spawnedQueen = true;
-            return true;
-        }
-
-        if (_queen?.Deleted != false)
-        {
-            _queen = null;
-            return false;
-        }
-
-        return true;
+        SpawnedQueen = true;
     }
 
     public override void AlterDamageScalarFrom(Mobile caster, ref double scalar)
     {
-        if (CheckQueen())
+        if (IsQueenAlive)
         {
             scalar *= 0.1;
         }

Projects/UOContent/Mobiles/Special/Neira.cs

@@ -163,13 +163,13 @@ public partial class Neira : BaseChampion
         }
     }
 
-    public override void AlterDamageScalarFrom(Mobile caster, ref double scalar)
+    public override void OnDamagedBySpell(Mobile from, int damage)
     {
-        base.AlterDamageScalarFrom(caster, ref scalar);
+        base.OnDamagedBySpell(from, damage);
 
         if (Utility.RandomDouble() < 0.1) // 10% chance to throw an unholy bone
         {
-            AddUnholyBone(caster, 1.0);
+            AddUnholyBone(from, 1.0);
         }
     }