ls: enable locale-aware decimal separator for -h/--human-readable

[arbelonson-source]

Summary

ls -lh's human-readable size column ignores LC_NUMERIC's decimal separator — it always shows e.g. 4.0K, even under a locale like fr_FR.UTF-8 where GNU ls -lh shows 4,0K. du -h and numfmt --to=iec already handle this correctly in this implementation.

Root cause: uucore::format::human::human_readable() has had locale-aware decimal-separator logic all along, gated behind the i18n-decimal uucore feature flag (localize_decimal, see src/uucore/src/lib/features/format/human.rs). du's and numfmt's Cargo.toml already enable that feature; ls's did not, so it silently compiled against the feature's no-op fallback and always used . regardless of locale.

Fix is a one-line addition of "i18n-decimal" to ls's uucore feature list in src/uu/ls/Cargo.toml, matching du and numfmt.

Fixes #14232

Test plan

• Added test_human_readable_uses_locale_decimal_separator in tests/by-util/test_ls.rs, asserting ls -lh under LC_ALL=fr_FR.UTF-8 shows 4,0K for a 4000-byte file
• Verified the new test fails against pre-fix code (reverted the Cargo.toml change locally, confirmed the test fails with 4.0K instead of 4,0K)
• cargo test --features feat_os_unix --test tests -- test_ls — 187 passed, 1 ignored (WASI-only)
• cargo clippy -p uu_ls --all-targets -- -D warnings — clean
• Manually verified against real GNU ls -lh under fr_FR.UTF-8, de_DE.UTF-8, and LC_NUMERIC=C (unaffected) — matches in all three cases

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AI-assisted-by: Claude Opus 5, via Claude Code

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/misc/io-errors (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Skip an intermittent issue tests/pr/bounded-memory (was skipped on 'main', now failing)