Add custom method .cpp files; update CXxxImpl headers with override stubs

- 12 .cpp files moved from source2toolkit-sdk (CBaseEntity, CCSPlayerController,
  etc.) with include paths updated from source2toolkit/schema/entity/classes/
  to schema/entity/classes/ (core include root)
- CXxxImpl headers regenerated: all custom methods now have inline override stubs
  delegating to Real()->Method() for each class with MANUAL_METHODS entries
- CBaseEntityImpl, CCSPlayerControllerImpl, etc. updated

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>