Refactor: Modularize boss custom modifier logic

[NotADucc]

• Added IModifierBoss.java interface to handle id checks and modifier fetches.
• Each boss now implements this interface in its own file, containing its modifier calculation.
  • This makes it easier to add new bosses without changing calculateHitOnNpc function, to add a boss append to the modifierBosses list inside XpDropDamageCalculator.java.
• Behavior should remain the same since I haven't changed any logic regarding calculating modifiers or NPC ids.
  • Tested in Delve 1-9 and CoX Tekton
  • NOT Tested in ToB/ToA

TLDR: Moved isXNpc and getModifier logic to their own files.