tests(pane): Add exhaustive capture_pane() flag tests

why: Ensure comprehensive coverage of all capture_pane() flag
combinations with parametrized test cases.

what:
- Add CapturePaneCase NamedTuple for test case definitions
- Add 16 parametrized test cases covering all flag variations
- Add backward compatibility test for existing code
- Add start/end parameters test with new flags
- Add trim_trailing warning test for tmux version check
- Use marker-based completion detection for reliability

Author: tony