feat(picker): add select_all and deselect_all methods and interactive keybindings

[miskatul-anwar]

Summary

Adds select_all() and deselect_all() helper methods and interactive keybindings to Picker for multiselect mode:

• Picker.select_all(): Selects all available options that are enabled (Option.enabled is not False).
• Picker.deselect_all(): Clears selected_indexes.
• Both methods safely return immediately if multiselect=False.
• Added interactive keybindings in Picker.run_loop:
  • a (KEYS_SELECT_ALL): Triggers select_all().
  • d (KEYS_DESELECT_ALL): Triggers deselect_all().

Testing

• Added unit test test_select_all_and_deselect_all in tests/test_pick.py.
• Ran full pytest test suite (all passing).
• Ran mypy type checks (clean).

[aisk]

Thanks for the PR. What's the intended use case for these methods? They aren't bound to any key in run_loop, so users can't trigger them interactively.

[miskatul-anwar]

Thanks for the feedback @aisk!

The initial motivation was programmatic batch selection (and custom key handlers), but interactive keybindings make multiselect mode much more convenient.

I've updated the PR to:

1. Bind default interactive key shortcuts in run_loop when multiselect=True:
   • a (KEYS_SELECT_ALL = (ord("a"),)): Selects all enabled options.
   • d (KEYS_DESELECT_ALL = (ord("d"),)): Deselects all options.
2. Clean up the trailing newline in tests/test_pick.py.