vfs: make lchmod update symlink mode

[trivikr]

Fixes: #64349

Fixes fs.promises.lchmod() on mounted VFS paths so it updates the symbolic
link's own mode instead of following the link and changing the target file mode.

This adds a non-following lchmodSync() provider operation for the memory and
real filesystem providers, and routes VFS promise lchmod() through it.

---

Assisted-by: openai:gpt-5.5

[codecov]

Codecov Report

❌ Patch coverage is 68.42105% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.25%. Comparing base (8e1ab55) to head (371f598).

Files with missing lines	Patch %	Lines
lib/internal/vfs/providers/real.js	45.45%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64350      +/-   ##
==========================================
+ Coverage   90.23%   90.25%   +0.01%     
==========================================
  Files         741      741              
  Lines      240979   240997      +18     
  Branches    45395    45401       +6     
==========================================
+ Hits       217450   217505      +55     
+ Misses      15112    15070      -42     
- Partials     8417     8422       +5     

Files with missing lines	Coverage Δ
lib/internal/vfs/file_system.js	99.37% <100.00%> (+0.15%)	⬆️
lib/internal/vfs/providers/memory.js	95.03% <100.00%> (+0.03%)	⬆️
lib/internal/vfs/providers/real.js	95.09% <45.45%> (-0.98%)	⬇️

... and 30 files with indirect coverage changes

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