uucore(fs): make display_permissions_unix cross-platform

[kaladron]

Remove the #[cfg(unix)] gate from display_permissions_unix and its helper get_file_display. Change the parameter from libc::mode_t to u32 (Metadata::mode() already returns u32, so no cast or information loss).

Add pub mod mode to uucore::fs with portable u32 constants for all POSIX S_I* values (S_IFMT, S_IFSOCK, S_IFLNK, S_IFREG, S_IFBLK, S_IFDIR, S_IFCHR, S_IFIFO, S_ISUID, S_ISGID, S_ISVTX, and all nine rwx bits). Callers can import uucore::fs::mode::* instead of libc, without requiring a Unix target.

Replace the has!() macro calls in display_permissions_unix with explicit bitwise & != 0 checks, which work without a type-specific macro.

Update chmod and mv to drop the libc::mode_t import and the as mode_t casts at each call site. Update is_stdin_directory to use mode::S_IFMT and mode::S_IFDIR instead of the libc imports.

Remove #[cfg(unix)] from test_display_permissions and test_get_file_display so both tests compile and run on all platforms.

[kaladron]

This is something I want for the uutils/tar code. Otherwise I will wind up duplicating this logic in the code and I think it would be better to combine them for making the code cross-platform for Unix and Windows.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/printf/printf-surprise is now being skipped but was previously passing.
Note: The gnu test tests/unexpand/bounded-memory is now being skipped but was previously passing.
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/rm/isatty (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[codspeed-hq]

Merging this PR will improve performance by 5.18%

⚡ 1 improved benchmark
✅ 301 untouched benchmarks
⏩ 46 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	cp_large_file[16]	279.2 µs	265.4 µs	+5.18%

---

_{Comparing kaladron:unix-fs (42db536) with main (319a06c)}

Footnotes

1. 46 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩