path: remove StringPrototypeCharCodeAt from more posix methods

[whoekage]

Summary

Extends the optimization landed in #54546 (posix.extname) to the remaining POSIX path methods still using StringPrototypeCharCodeAt. #54668 covers resolve/normalize/parse; this PR covers dirname, basename, and relative.

What changed

Replaced StringPrototypeCharCodeAt(path, i) === CHAR_FORWARD_SLASH with path[i] === '/' in three POSIX methods. Diff: +12 / −14 lines in lib/path.js.

Benchmark

Apple M1, 30 runs via benchmark/compare.js. Showing significant cases:

dirname-posix

path	delta	sig
/foo	+12.45%	***
/foo/bar/baz/asdf/quux	+8.82%	***
/foo/bar	+8.82%	***
foo	+6.34%	*
foo/bar	+2.26%	*

basename-posix

pathext	delta	sig
/foo/bar/baz/asdf/quux.html|.html	+8.38%	***
/foo/.bar.baz|.baz	+8.25%	***
/foo/.bar.baz	+6.90%	***
foo/bar.	+5.94%	***
foo	+5.78%	*

relative-posix

paths	delta	sig
/var|/bin	+3.28%	**

Methodology validation

Control benchmark on extname-posix (unchanged in this PR) shows ±2% deltas without statistical significance, confirming methodology. No regressions on Win32 paths (slow path untouched).

Test plan

• parallel/test-path* — all 17 pass
• parallel/test-url-* — all 15 pass
• parallel/test-fs-readfile/stat/realpath — pass
• parallel/test-module-* — all 32 pass
• Fuzz: 425 input cases identical to baseline
• make lint-js — clean

Refs: #54546, #54668

[nodejs-github-bot]

Review requested:

• @nodejs/path

[whoekage]

Hi! Could a collaborator start CI here when convenient? The change is small
(+12/-14) and the path tests pass locally.

This extends the same StringPrototypeCharCodeAt(...) === CHAR_* to
path[i] === '*' conversion that was already accepted in #54546 (merged,
posix.extname) and is in progress in #54668, applied to the remaining posix
methods.

Related C++ path optimization: #63753.

Thanks!

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/75680/

[trivikr]

@whoekage Can you sign your commit and force push?

It's required as per updated instructions

Your commit must contain the Signed-off-by line with your name and email address as an acknowledgement that you agree to the Developer Certificate of Origin

[whoekage]

@trivikr Done.
Signed off and force-pushed. The diff is unchanged, only the commit message now carries the Signed-off-by line. Could you kick off a fresh CI run when you get a chance?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.06%. Comparing base (79def6d) to head (3b3bb25).
⚠️ Report is 1081 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63662      +/-   ##
==========================================
- Coverage   90.32%   90.06%   -0.26%     
==========================================
  Files         732      751      +19     
  Lines      236435   254418   +17983     
  Branches    44527    47964    +3437     
==========================================
+ Hits       213563   229151   +15588     
- Misses      14589    16446    +1857     
- Partials     8283     8821     +538     

Files with missing lines	Coverage Δ
lib/path.js	97.48% <100.00%> (-0.01%)	⬇️

... and 442 files with indirect coverage changes

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[trivikr]

Benchmark CI: https://ci.nodejs.org/view/Node.js%20benchmark/job/benchmark-node-micro-benchmarks/1892/