- Add: Adds `.tui.main.UNKNOWN` constant for `scan_dir_*` functions.
- Change: Updates `.tui.main.sort_key_lexi()`.
  - Now accepts `os.DirEntry` or `pathlib.Path` instances instead of strings.
- Change: Updates `.tui.main.scan_dir_entry()`.
  - Now accepts `os.DirEntry` or `pathlib.Path` instances instead of strings for directory entries.
  - Other minor performance optimizations.
- Change: Significantly improves directory entry sorting and scanning performance.
  - Leverages `os.DirEntry`'s stat caching to eliminate system calls by `os.path.isfile()`.
- Change: Updates docstrings.

- Change: Updates `.tui.main.scan_dir()`.
  - Adds *last_entry* and *sort_key* parameters for improved functionality.
  - Replaces `os.listdir()` with `os.scandir()` for significant performance improvements.
  - Now yeilds the entry typecode along with the item tuple.
  - Now yeilds all scanned entries, no matter the type to allow for better control within it's caller.
- Change: Updates docstrings.

- Change: Updates `scan_dir_grid()` and `scan_dir_menu()` in `.tui.main`.
  - Both functions now utilize `.tui.main.scan_dir()`.
- Change: Updates docstrings.

- Fix: Fixed `scan_dir_grid()` appending to the grid scan list after the grid has changed.
  - Occured when switching to an empty grid before the current grid scan is done.
  - `scan_dir_grid()` now uses an alias to the grid scan list, which is updated (with `.tui.main._grid_list`) only when changing grids.
- Change: Renamed `.tui.main.grid_list` to `.tui.main._grid_list`.

- Change: Grouped directories before files.
- Change: Removed unnecessary code.
- Change: Updated docstrings and comments.