fs: keep timestamps of files skipped by cpSync

[christianaurichzm]

With force: false and preserveTimestamps: true, cpSync() updates the timestamps of an existing destination file even though the file itself is skipped.

This only affects the C++ recursive copy path used by cpSync() without a filter. The JS paths used with a filter, fs.cp(), and fs.promises.cp() already leave skipped files untouched.

const fs = require('node:fs');

fs.mkdirSync('src');
fs.mkdirSync('dest');

fs.writeFileSync('src/f', 'new');
fs.utimesSync('src/f', 1000, 1000);

fs.writeFileSync('dest/f', 'old');
fs.utimesSync('dest/f', 2e9, 2e9);

fs.cpSync('src', 'dest', {
  recursive: true,
  force: false,
  preserveTimestamps: true,
});

console.log(
  fs.readFileSync('dest/f', 'utf8'),
  fs.statSync('dest/f').mtimeMs,
);

// old 1000000
// expected: old 2000000000000

In CopyDirRecursive(), copy_file() returns false when skip_existing causes the copy to be skipped. The mode restoration already checks that return value, but CopyUtimes() did not.

Only copy timestamps when the file was actually copied.

The test covers both the C++ path and the filter path. It fails on main and passes with this change.

make lint and test-fs-* pass on x64 Linux. v22.x is affected as well.

#65547 touches the same loop, but skipped files still leave copied as false, so this change applies cleanly on top of it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.39%. Comparing base (4bd56b3) to head (b1135e9).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66305      +/-   ##
==========================================
+ Coverage   90.37%   90.39%   +0.01%     
==========================================
  Files         790      790              
  Lines      274279   274272       -7     
  Branches    52506    52512       +6     
==========================================
+ Hits       247870   247915      +45     
+ Misses      16890    16837      -53     
- Partials     9519     9520       +1     

Files with missing lines	Coverage Δ
src/node_file.cc	75.21% <100.00%> (+0.02%)	⬆️

... and 35 files with indirect coverage changes

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