feat(picker): support negative default_index, select_all/deselect_all, and prevent marking disabled options

[miskatul-anwar]

Summary

This PR introduces negative index support, batch selection methods, and disabled option safety to pick:

1. Negative default_index Support (src/pick/__init__.py):

   • Added support for negative default indices (e.g. default_index=-1 to select the last option by default), adhering to standard Python indexing behavior.

2. Disabled Option Guard in mark_index():

   • mark_index() now explicitly verifies that the target option is enabled before modifying selected_indexes. This prevents disabled options from being marked if mark_index() is invoked programmatically or by keypress.

3. select_all() & deselect_all() Helper Methods:

   • Added select_all() and deselect_all() methods to Picker for multiselect mode. select_all() selects all enabled options while respecting disabled option status.

4. Standalone cadule Import Fallback:

   • Added a graceful try...except ImportError fallback for cadule import so pick can run in standalone mode without build artifact errors.

Testing & Verification

Ran test suite:

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