vfs: fix VirtualReadStream race with async iteration

[Y1D7NG]

Fixes: #64377

VirtualReadStream opened files on the next tick without _construct, so for-await and pipeline could read before the fd was ready and fail with EBADF. Open the virtual file in _construct instead, matching fs.ReadStream.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.25%. Comparing base (8fec65d) to head (31569ec).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #64394   +/-   ##
=======================================
  Coverage   90.25%   90.25%           
=======================================
  Files         741      741           
  Lines      241207   241196   -11     
  Branches    45430    45436    +6     
=======================================
- Hits       217698   217693    -5     
+ Misses      15084    15071   -13     
- Partials     8425     8432    +7     

Files with missing lines	Coverage Δ
lib/internal/vfs/streams.js	95.32% <100.00%> (-0.15%)	⬇️

... and 26 files with indirect coverage changes

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