feat: support GNU ls -f as shorthand for -a -U

[MsfPablo]

Closes #1181.

GNU ls accepts -f, which lists entries in directory order (no sorting) and does not hide dotfiles. lsd rejected it outright:

$ lsd -f
error: unexpected argument '-f' found

This breaks alias ls=lsd whenever a script or tool emits ls -f.

Change

Adds -f as a short-only flag meaning "do not sort, and show hidden entries" — equivalent to -a -U:

• src/app.rs: new no_sort_all arg with the same overrides_with_all list as -U, so an explicit sort flag given later still wins (lsd -f -t sorts by time, lsd -t -f does not sort), matching GNU's last-one-wins behaviour.
• src/flags/display.rs: -f implies Display::All (-A still takes precedence, as it does over -a).
• src/flags/sorting.rs: -f implies SortColumn::None.
• doc/lsd.md: documented.

Scope kept to what the issue asks: GNU's -f also disables --color and -l, but that felt out of scope and unhelpful for lsd, so it is not replicated. Happy to add it if maintainers prefer full parity.

Tests

Unit tests for Display::from_cli and SortColumn::from_cli (including both -f -t / -t -f orderings) plus an integration test asserting -f lists hidden entries.

$ cargo test
   ... 394 passed; 0 failed        (unit)
   ... 43 passed; 1 failed         (integration)
$ cargo fmt --check   # clean
$ cargo clippy --all-targets   # 7 warnings, identical to the count on unmodified master

The single integration failure is test_date_custom_format_supports_nanos_with_length, which fails identically on unmodified master in my environment (locale uses , as the decimal separator) — pre-existing and unrelated; see #1227 / #1230.

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Disclosure: this patch was written with AI assistance (Claude). I reviewed the diff and ran the full verification above locally.