fix(fs): do not apply exts filter to directory entries

[LeSingh1]

Summary

Fixes #6736

When includeDirs is true (the default) and the exts option is set, directory entries were incorrectly being filtered out by the exts check because directories have no file extension. This meant that using walk(path, { exts: ['.ts'] }) would not yield any directory entries at all, even though includeDirs defaults to true.

Before:

// Structure: mydir/ x.ts  subdir/  subdir/y.rs
Array.from(walk("mydir", { exts: [".ts"] }))
// => [{ path: "mydir/x.ts", ... }]
// Root dir and subdir are missing!

After:

Array.from(walk("mydir", { exts: [".ts"] }))
// => [
//   { path: "mydir", isDirectory: true, ... },       // root dir included
//   { path: "mydir/x.ts", isFile: true, ... },       // .ts file included
//   { path: "mydir/subdir", isDirectory: true, ... }, // subdir included
//   // mydir/subdir/y.rs excluded (not .ts)
// ]

Changes

• fs/walk.ts: When yielding a directory entry (for the root path in both walk and walkSync), pass undefined for exts to the include() helper so that directory paths are not subject to the file-extension filter. The match and skip regexp filters still apply to directories.
• fs/walk_test.ts: Updated the existing exts tests to include the root directory "." in expected results. Added two new tests (walk() and walkSync()) verifying that subdirectories are included when the exts option is set.
• fs/testdata/walk/ext_with_subdir/: New testdata directory with x.ts and subdir/y.rs to exercise the subdirectory case.

Test plan

• Existing exts tests now include the root dir "." in expected results
• New tests walk() includes subdirs when using exts option and walkSync() includes subdirs when using exts option pass
• All other walk tests continue to pass

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.65%. Comparing base (f0431c2) to head (284b140).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7186      +/-   ##
==========================================
+ Coverage   94.64%   94.65%   +0.01%     
==========================================
  Files         629      628       -1     
  Lines       51895    51640     -255     
  Branches     9373     9323      -50     
==========================================
- Hits        49116    48880     -236     
+ Misses       2211     2198      -13     
+ Partials      568      562       -6     

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[bartlomieju]

Two suggestions before merge:

1. Update the exts JSDoc to reflect the new behavior. The option docs in fs/walk.ts still say:

List of file extensions used to filter entries. If specified, entries without the file extension specified by this option are excluded.

That's now inaccurate for directories, which is exactly what this PR changes. Worth adding a clarifying sentence, e.g.:

Directory entries are not subject to this filter, since directories have no file extension.

2. Test data duplication (optional). The new fs/testdata/walk/ext_with_subdir/ fixtures (x.ts, subdir/y.rs) largely duplicate the existing fs/testdata/walk/ext/ setup. Extending the existing ext/ directory with a subdir could avoid the extra fixture dir — though a dedicated fixture is also perfectly readable, so feel free to keep it if you prefer the isolation.

Otherwise the fix looks correct and complete: because walk recurses with each subdirectory as the new root, the single-line change at the recursion entry point correctly fixes directory inclusion at every depth, not just the top level.