fix(child_process): add execArgv support to spawn()

[dajiaohuang]

Fix issue #65725 where spawn() silently ignores the execArgv option.

spawn() now correctly handles execArgv by prepending it to the args array, matching fork() behavior.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.98%. Comparing base (09f5aae) to head (60e112d).
⚠️ Report is 20 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65741      +/-   ##
==========================================
+ Coverage   89.96%   89.98%   +0.02%     
==========================================
  Files         757      757              
  Lines      257376   257384       +8     
  Branches    48794    48794              
==========================================
+ Hits       231550   231619      +69     
+ Misses      16911    16846      -65     
- Partials     8915     8919       +4     

Files with missing lines	Coverage Δ
lib/child_process.js	94.16% <100.00%> (+0.04%)	⬆️

... and 35 files with indirect coverage changes

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[Renegade334]

This would imply that spawn() is just for creating Node.js processes. It's not, it's for arbitrary child processes, and Node.js CLI arguments should be passed positionally.

[MikeMcC399]

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