Fixes: Anvil Rename Bug + Arcane Archer Variant
1) Anvil Rename Bug (vanilla renaming broken)
Problem
Players couldn’t rename items in the anvil.
The result item would appear for a second and then disappear.

Cause
The anvil listener was clearing the result whenever either input slot was empty:

• Vanilla rename uses only the left slot (right slot is empty).
• The plugin logic treated right == null as invalid and forced event.setResult(null).

Fix
Allow vanilla anvil operations when the right slot is empty.

Before (buggy logic) ```java if (left == null || right == null) { event.setResult(null); return; }