fix: Fixes double calls with Target cancel and spell sequences (#1840)

### Summary
- Cleans up target cancellation being called incorrectly.
- An invalid target type (which should never happen), now calls `OnTargetUntargetable` instead of `OnTargetCanceled`
- Removes double calls to `FinishSequence` in Spells.

Projects/UOContent/Spells/Necromancy/BloodOathSpell.cs

@@ -92,8 +92,6 @@ public class BloodOathSpell : NecromancerSpell, ISpellTargetingMobile
             _table[m] = timer;
             HarmfulSpell(m);
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()
@@ -156,4 +154,4 @@ public class BloodOathSpell : NecromancerSpell, ISpellTargetingMobile
             }
         }
     }
-}
+}

Projects/UOContent/Spells/Necromancy/CorpseSkin.cs

@@ -91,8 +91,6 @@ public class CorpseSkinSpell : NecromancerSpell, ISpellTargetingMobile
 
             HarmfulSpell(m);
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()
@@ -141,4 +139,4 @@ public class CorpseSkinSpell : NecromancerSpell, ISpellTargetingMobile
             DoExpire();
         }
     }
-}
+}

Projects/UOContent/Spells/Necromancy/EvilOmen.cs

@@ -66,8 +66,6 @@ public class EvilOmenSpell : NecromancerSpell, ISpellTargetingMobile
 
             BuffInfo.AddBuff(m, new BuffInfo(BuffIcon.EvilOmen, 1075647, 1075648, duration, m));
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()
@@ -85,4 +83,4 @@ public class EvilOmenSpell : NecromancerSpell, ISpellTargetingMobile
 
         return false;
     }
-}
+}

Projects/UOContent/Spells/Necromancy/MindRot.cs

@@ -59,8 +59,6 @@ public class MindRotSpell : NecromancerSpell, ISpellTargetingMobile
 
             HarmfulSpell(m);
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()
@@ -133,4 +131,4 @@ public class MRExpireTimer : Timer
             Stop();
         }
     }
-}
+}

Projects/UOContent/Spells/Necromancy/PainSpike.cs

@@ -81,8 +81,6 @@ public class PainSpikeSpell : NecromancerSpell, ISpellTargetingMobile
             // SpellHelper.Damage( this, m, damage, 100, 0, 0, 0, 0, Misc.DFAlgorithm.PainSpike );
             HarmfulSpell(m);
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()
@@ -114,4 +112,4 @@ public class PainSpikeSpell : NecromancerSpell, ISpellTargetingMobile
             BuffInfo.RemoveBuff(_mobile, BuffIcon.PainSpike);
         }
     }
-}
+}

Projects/UOContent/Spells/Necromancy/PoisonStrike.cs

@@ -142,12 +142,10 @@ public class PoisonStrikeSpell : NecromancerSpell, ISpellTargetingMobile
                 }
             }
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()
     {
         Caster.Target = new SpellTargetMobile(this, TargetFlags.Harmful, Core.ML ? 10 : 12);
     }
-}
+}

Projects/UOContent/Spells/Necromancy/Strangle.cs

@@ -107,8 +107,6 @@ public class StrangleSpell : NecromancerSpell, ISpellTargetingMobile
 
         var t_Duration = TimeSpan.FromSeconds(length);
         BuffInfo.AddBuff(m, new BuffInfo(BuffIcon.Strangle, 1075794, 1075795, t_Duration, m, args));
-
-        FinishSequence();
     }
 
     public override void OnCast()
@@ -226,4 +224,4 @@ public class StrangleSpell : NecromancerSpell, ISpellTargetingMobile
             }
         }
     }
-}
+}

Projects/UOContent/Spells/Necromancy/VengefulSpirit.cs

@@ -62,8 +62,6 @@ public class VengefulSpiritSpell : NecromancerSpell, ISpellTargetingMobile
                 rev.FixedParticles(0x373A, 1, 15, 9909, EffectLayer.Waist);
             }
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()
@@ -86,4 +84,4 @@ public class VengefulSpiritSpell : NecromancerSpell, ISpellTargetingMobile
 
         return true;
     }
-}
+}