perf_hooks: reuse buffer for uv metrics

[HoonDongKang]

Summary

Previously, each access to performance.nodeTiming.uvMetricsInfo allocated a new V8 array. This change reuses an AliasedInt32Array shared between C++ and JavaScript while preserving the existing public API behavior.

The shared buffer is cleared before snapshot serialization and restored during deserialization so both sides continue to reference the same memory.

Benchmark

                                                                confidence   improvement   accuracy (*)    (**)   (***)
perf_hooks/nodetiming-uvmetricsinfo.js events=1 n=1000000      ***           +158.99 %   ±12.43%  ±16.73%  ±22.15%
perf_hooks/nodetiming-uvmetricsinfo.js events=1000 n=1000000   ***           +167.65 %   ±6.95%  ±9.32%  ±12.29%
perf_hooks/nodetiming-uvmetricsinfo.js events=10000 n=1000000  ***           +162.19 %   ±7.61%  ±10.22%  ±13.51%

                                                                  -174.6%            0%            +174.6%
perf_hooks/nodetiming-uvmetricsinfo.js events=1 n=1000000                          |█████████████████░░  +158.99% ***
perf_hooks/nodetiming-uvmetricsinfo.js events=1000 n=1000000                       |██████████████████░  +167.65% ***
perf_hooks/nodetiming-uvmetricsinfo.js events=10000 n=1000000                      |██████████████████   +162.19% ***

Tests

• test-performance-nodetiming-uvmetricsinfo
• test-performance-nodetiming
• test-perf-hooks-worker-timeorigin
• test-perf-hooks
• test-snapshot-api

Assisted-by: Codex

[nodejs-github-bot]

Review requested:

• @nodejs/startup

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.19%. Comparing base (5552a06) to head (188975e).
⚠️ Report is 113 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #65985    +/-   ##
========================================
  Coverage   90.18%   90.19%            
========================================
  Files         771      771            
  Lines      264622   265501   +879     
  Branches    50222    50484   +262     
========================================
+ Hits       238659   239456   +797     
- Misses      16964    16986    +22     
- Partials     8999     9059    +60     

Files with missing lines	Coverage Δ
lib/internal/perf/nodetiming.js	94.31% <100.00%> (+0.03%)	⬆️
src/node_perf.cc	87.25% <100.00%> (+0.58%)	⬆️
src/node_snapshotable.cc	73.53% <100.00%> (ø)

... and 111 files with indirect coverage changes

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