vfs: fix path returned by recursive mkdir

[watilde]

mkdir() with recursive: true returns the first directory that was created. VFS passed the provider's return value straight through, so the path came back in the wrong namespace: RealFSProvider returned an absolute path inside its root, leaking that root to the caller, and a mounted VFS returned a VFS-internal path without the mount point.

Map the created path back through the provider and mount translations so the returned value is a path the caller can hand to fs again. This covers the sync, callback, and promises forms.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.30%. Comparing base (dc7838c) to head (819ceed).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #65062   +/-   ##
=======================================
  Coverage   90.30%   90.30%           
=======================================
  Files         759      759           
  Lines      247629   247644   +15     
  Branches    46688    46701   +13     
=======================================
+ Hits       223618   223636   +18     
- Misses      15469    15473    +4     
+ Partials     8542     8535    -7     

Files with missing lines	Coverage Δ
lib/internal/vfs/file_system.js	99.37% <100.00%> (+<0.01%)	⬆️
lib/internal/vfs/providers/real.js	95.32% <100.00%> (+0.23%)	⬆️

... and 30 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.