feat: Adds ability groups, DOT abilities, and combat abilities (#1264)

- [X] Adds `MonsterAbilitySingleTarget`
- [X] Adds `MonsterAbilitySingleTargetDoT`
- [X] Adds monster ability groups with weighted abilities
- [X] Adds rune corruption ability
- [X] Adds poison gas counter ability
- [X] Adds stun attack ability
- [X] Adds throw hatchet counter ability
- [X] Adds fanning fire ability
- [X] Fixes destroy equipment to skip spell channel items

Projects/UOContent/Mobiles/Abilities/MonsterAbilitySingleTargetDoT.cs

@@ -0,0 +1,79 @@
+using System;
+using System.Collections.Generic;
+
+namespace Server.Mobiles;
+
+public abstract class MonsterAbilitySingleTargetDoT : MonsterAbilitySingleTarget
+{
+    private Dictionary<Mobile, ExpireTimer> _table;
+
+    public virtual TimeSpan MinDelay => TimeSpan.FromSeconds(10.0);
+    public virtual TimeSpan MaxDelay => TimeSpan.FromSeconds(10.0);
+
+    protected override void OnTarget(MonsterAbilityTrigger trigger, BaseCreature source, Mobile defender)
+    {
+        _table ??= new Dictionary<Mobile, ExpireTimer>();
+
+        var duration = Utility.RandomMinMax(MinDelay, MaxDelay);
+        var count = GetCount(source, defender);
+        var timer = _table[defender] = new ExpireTimer(this, source, defender, duration, count);
+        timer.Start();
+
+        StartEffect(source, defender);
+    }
+
+    protected virtual int GetCount(BaseCreature source, Mobile defender) => 1;
+
+    protected abstract void StartEffect(BaseCreature source, Mobile defender);
+
+    protected virtual void EffectTick(BaseCreature source, Mobile defender, out TimeSpan nextDelay)
+    {
+        nextDelay = Utility.RandomMinMax(MinDelay, MaxDelay);
+    }
+
+    protected abstract void EndEffect(BaseCreature source, Mobile defender);
+    protected abstract void OnEffectExpired(BaseCreature source, Mobile defender);
+
+    public bool IsUnderEffect(Mobile defender) => _table?.ContainsKey(defender) == true;
+
+    protected bool RemoveEffect(BaseCreature source, Mobile defender)
+    {
+        if (_table?.Remove(defender, out var timer) == true)
+        {
+            timer.Stop();
+            EndEffect(source, defender);
+            return true;
+        }
+
+        return false;
+    }
+
+    private class ExpireTimer : Timer
+    {
+        private BaseCreature _source;
+        private Mobile _defender;
+        private MonsterAbilitySingleTargetDoT _ability;
+
+        public ExpireTimer(
+            MonsterAbilitySingleTargetDoT ability,
+            BaseCreature source,
+            Mobile defender,
+            TimeSpan delay,
+            int count
+        ) : base(delay, delay, count)
+        {
+            _ability = ability;
+            _source = source;
+            _defender = defender;
+        }
+
+        protected override void OnTick()
+        {
+            _ability.EffectTick(_source, _defender, out var delay);
+            Delay = delay;
+
+            _ability.RemoveEffect(_source, _defender);
+            _ability.OnEffectExpired(_source, _defender);
+        }
+    }
+}