fix(fs): prevent ENOENT on subst drive root paths like "M:\\" on Windows

[mag123c]

This PR fixes an issue where fs.readdirSync('M:\\') and related calls would fail with an ENOENT error on Windows when using subst drive roots.

Previously, Node.js added a trailing backslash (\) even when the input path was already a drive root (e.g., M:\ or \\?\M:\), resulting in invalid paths like M:\\\. This patch introduces a check to detect standard and namespaced drive root formats and avoid appending an extra slash in those cases.

The fix is Windows-specific and scoped only to the logic within fs.readdir.

Changes

• Updated src/node_file.cc to detect and skip appending \ for drive root paths
• Added regression test: test/parallel/test-fs-readdir-windows-subst.js
• Covers subst-like paths with and without trailing slashes
• Verifies no ENOENT error is thrown for valid drive roots

Context

Fixes: #58970

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.05%. Comparing base (4bfcad1) to head (c97462b).
⚠️ Report is 732 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #58989 +/- ##
==========================================
- Coverage 90.14% 90.05% -0.09% 
==========================================
Files 630 645 +15 Lines 186784 189130 +2346 Branches 36653 37089 +436 ==========================================
+ Hits 168377 170327 +1950 - Misses 11205 11511 +306 - Partials 7202 7292 +90 

Files with missing lines	Coverage Δ
src/node_file.cc	75.90% <100.00%> (-1.08%)	⬇️

... and 245 files with indirect coverage changes

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[mag123c]

I've force-pushed a fix (e.g. lint issue resolved).

[mag123c]

I apologize - the format-cpp check failed again. I've pushed another fix to address the formatting issue.
However, the test-macOS job is failing with a timeout in test-fs-promises-watch-iterator.js:

This appears to be an unrelated test, as:

• My changes are Windows-specific and wrapped in #ifdef _WIN32

[github-actions]

Failed to start CI

 ⚠ No approving reviews found
✘ Refusing to run CI on potentially unsafe PR

https://github.com/nodejs/node/actions/runs/16441290676

[StefanStojanovic]

Approving to enable starting the CI. Still not approved to land AFAIC.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/68103/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/68416/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/68787/

[StefanStojanovic]

Hello @mag123c what's the status on this? Are there still some changes to be implemented before reviewing?

[mag123c]

@StefanStojanovic
Added a refactoring commit to optimize the drive root detection

• Removed redundant length checks
• Replaced substr() with direct indexing

Ready for review.

[mag123c]

@StefanStojanovic
Because of conflict, I checked and tracked the change code,
I Think closing this PR as the issue has already been fixed in upstream via PR #59847

The upstream fix uses a simpler approach: if (slashCheck && !path.ToStringView().ends_with("\\")) which achieves the same result with less code.