0.7.1

Change all slot type hints to use string keys

Updated all type hints throughout the codebase to consistently use string
keys for slot identifiers instead of int or int|str.

Changes:
- __init__.py: Changed curr_slots, new_slots, slots_to_add, slots_to_remove
  from dict[int, Any] to dict[str, Any]
- providers/_base.py: Changed get_usercodes() return type from
  dict[int, int|str] to dict[str, int|str]
- providers/virtual.py: Updated async_get_usercodes() return type and
  removed int() conversion to keep keys as strings
- providers/zwave_js.py: Updated async_get_usercodes() to use string keys,
  changed code_slots iterator to yield strings, and updated all references
  to use code_slot_key (string) instead of code_slot (int)

This ensures consistency with the coordinator which already converts all
keys to strings, and properly supports non-numeric slot identifiers like
'A', 'B', etc.

All tests passing.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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