fix: Removes side effect of setting skill mod when changing Owner (#1101)

## Breaking Change!
Setting `mod.Owner` will no longer update a skill mod.
**Please stick to the API and use `mobile.AddSkillMod(mod)` for all situations, including equipping.**


## Fixes
- [X] Fixes memory leak in factions.
- [X] Changes `List<SkillMod>` to `HashSet<SkillMod>`.
- [X] Eliminates skill mods adding/removing twice.

Projects/Server/Mobiles/Mods/SkillMod.cs

@@ -13,6 +13,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
  *************************************************************************/
 
+using System.Runtime.CompilerServices;
 using ModernUO.Serialization;
 
 namespace Server;
@@ -50,21 +51,6 @@ public abstract partial class SkillMod : MobileMod
         }
     }
 
-    public override Mobile Owner
-    {
-        get => base.Owner;
-        set
-        {
-            var owner = base.Owner;
-            if (owner != value)
-            {
-                owner?.RemoveSkillMod(this);
-                base.Owner = owner = value;
-                owner?.AddSkillMod(this);
-            }
-        }
-    }
-
     [SerializableField(1)]
     public SkillName Skill
     {
@@ -136,10 +122,8 @@ public abstract partial class SkillMod : MobileMod
         }
     }
 
-    public void Remove()
-    {
-        Owner = null;
-    }
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void Remove() => Owner?.RemoveSkillMod(this);
 
     public abstract bool CheckCondition();
 }