Re-sort file tree when sort mode changes

[lorenjphillips]

Noticed the file tree sort mode wasnt actually re-sorting when you switched modes - you had to collapse and re-expand directories to see the change. Found the TODO comment at view.rs:268 and figured I'd take a crack at it.

Changes

• Added SortMode::comparator() that returns the right comparison fn for each mode
• Added FileTree::sort_all_nodes() to re-sort all expanded directories
• Updated set_sort_mode() to trigger the resort

Testing

• added two tests for the sort mode switching behavior
• ran cargo test file_tree - all 36 tests pass
• built with cargo build --lib, no new warnings

Let me know if you want me to change anythign!

[sinelaw]

Where in the UI can I see the effect of this change?

[lorenjphillips]

Thanks for reviewing this! sort mode isn't wired up to any keybinding yet... I added the fix first figuring the UI part would be simpler to add on top, happy to add what I built for myself but figured you may be opinionated about UI :)

Where in the UI can I see the effect of this change?

[sinelaw]

Gotcha I'll take a look at adding sort to the file explorer ui

[lorenjphillips]

Thanks so much!! Let me know if you would like any more changes in the PR for the sort!!