rm: fix path parsing for dot/dotdot protection

[naoNao89]

Fix rm -rf ./ silently deleting contents. Improves path_is_current_or_parent_directory() to properly detect paths like ./, ../, d/., etc.

Added robust byte-level path parsing and comprehensive tests

Fixes #9749.

Future Work (maybe)

• --preserve-root=all mount point detection
• FTS traversal (safer directory walking)
• Directory status caching (DS_EMPTY, DS_NONEMPTY)
  would require significant refactoring and are outside of PR

[github-actions]

GNU testsuite comparison:

Note: The gnu test tests/pr/bounded-memory is now being skipped but was previously passing.
Congrats! The gnu test tests/cp/link-heap is now passing!

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cut/bounded-memory. tests/cut/bounded-memory is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/printf/printf-surprise is now being skipped but was previously passing.
Congrats! The gnu test tests/cp/link-heap is now passing!

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/tail/pipe-f is now being skipped but was previously passing.
Congrats! The gnu test tests/cp/link-heap is now passing!

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/csplit/csplit-heap is now being skipped but was previously passing.
Note: The gnu test tests/seq/seq-epipe is now being skipped but was previously passing.
Congrats! The gnu test tests/cp/link-heap is now passing!

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cut/bounded-memory is no longer failing!
Note: The gnu test tests/unexpand/bounded-memory is now being skipped but was previously passing.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/date/date-locale-hour. tests/date/date-locale-hour is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/rm/isatty. tests/rm/isatty is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/cut/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/cut/cut-huge-range is now being skipped but was previously passing.
Congrats! The gnu test tests/seq/seq-epipe is now passing!

[codspeed-hq]

Merging this PR will not alter performance

✅ 309 untouched benchmarks
⏩ 46 skipped benchmarks¹

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_{Comparing naoNao89:rm-dot-protection-9749 (cb45f75) with main (0a9fc3e)²}

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. ↩

2. No successful run was found on main (07d6f27) during the generation of this report, so 0a9fc3e was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩