Add comprehensive helix-like modal key bindings system for fish shell
with:
- New `fish_helix_key_bindings` function with helix-inspired navigation
- Modal editing support with count modifiers via `fish_bind_count`
- Visual mode prompt indicator via `fish_default_mode_prompt`
- Enhanced clipboard integration with proper notification formatting
The implementation provides vim/helix-style modal editing while
maintaining
fish shell compatibility and includes proper mode indicators, count
tracking,
and seamless integration with existing fish key binding systems.
