Add support for horse-type inventories & refactor sorting system to check "safe" slots for sorting on

[kuroneko007]

Added a HorseScreenMixin to handle sorting of horse-type inventories. This caused various issues due to the horse's own armor & saddle slots that required a rework of the sorting slot identification system. It should now be much more robust and work for any kind of container.

• Added safe slot detection logic
  - Introduced a new getSafeSlots() method that builds a mapping of valid container slot indices.
  - Skips slots that can’t hold normal items (e.g. saddle, armor, or other equipment slots).
  - Uses slot behavior (canInsert, getMaxItemCount, isEnabled) rather than hardcoding item names.

• Refactored core sorting logic
  - combineLikeStacks() and sort() now work from the safeSlots list rather than raw index offsets.
  - Prevents mismatched clicks caused by filtered slots.

• Improved click safety
  - Integrated handling for SkippedUnsafeClickException across all operations.
  - Automatically clears the cursor and resynchronizes the snapshot after any skipped click.
  - Prevents floating stacks under the mouse and desyncs with the actual inventory state.

• Enhanced clearMouseStack()
  - Now finds the first safe empty slot that can accept the cursor stack.
  - Avoids attempting to place items into invalid equipment slots.

Testing

✅ Donkey inventory with equipped saddle and chest — sorts chest slots correctly, saddle untouched.

✅ Mule and horse inventories verified.

✅ Normal chests, player inventory, and modded containers unaffected.

✅ No floating cursor or mismatched stacks.

Impact

This update makes the sorting system significantly more reliable across all container types, especially mixed player + entity inventories.
It also lays groundwork for future mod support — safe-slot detection now adapts automatically to new container layouts without needing hardcoded exclusions.