src: replace Environment::GetCurrent with args.GetIsolate

[KimSH39]

Refactor code in node_util.cc and uv.cc to remove unnecessary
calls to Environment::GetCurrent(args), which reduces extra lookups
and makes the code clearer.

• Use args.GetIsolate() instead of env->isolate()
• Use isolate->GetCurrentContext() instead of env->context()
• Verified by running the full test suite.

[codecov]

Codecov Report

❌ Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.28%. Comparing base (58f408f) to head (d3508ca).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_util.cc	85.00%	1 Missing and 2 partials ⚠️
src/uv.cc	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #59876      +/-   ##
==========================================
- Coverage   88.29%   88.28%   -0.01%     
==========================================
  Files         702      702              
  Lines      206875   206866       -9     
  Branches    39797    39807      +10     
==========================================
- Hits       182655   182628      -27     
- Misses      16226    16256      +30     
+ Partials     7994     7982      -12     

Files with missing lines	Coverage Δ
src/uv.cc	90.62% <85.71%> (ø)
src/node_util.cc	79.80% <85.00%> (-0.57%)	⬇️

... and 26 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/69230/