process: handle closed stdio in execve

[Archkon]

Treat EBADF while preparing standard file descriptors as an indication that the descriptor is already closed instead of failing execve.

Skip closed descriptors during flag restoration, check restoration errors

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.29%. Comparing base (985aa07) to head (f574e9e).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_process_methods.cc	33.33%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65133      +/-   ##
==========================================
- Coverage   90.31%   90.29%   -0.03%     
==========================================
  Files         759      759              
  Lines      248299   248301       +2     
  Branches    46854    46863       +9     
==========================================
- Hits       224251   224200      -51     
- Misses      15468    15512      +44     
- Partials     8580     8589       +9     

Files with missing lines	Coverage Δ
src/node_process_methods.cc	88.24% <33.33%> (-0.29%)	⬇️

... and 37 files with indirect coverage changes

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