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 88.53%. Comparing base (e105e82) to head (bd240cb).
⚠️ 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   88.53%   88.53%           
=======================================
  Files         704      704           
  Lines      208087   208078    -9     
  Branches    40006    40012    +6     
=======================================
+ Hits       184223   184230    +7     
+ Misses      15869    15863    -6     
+ Partials     7995     7985   -10     

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 27 files with indirect coverage changes

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[nodejs-github-bot]

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

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/69675/