refactor: use inspector API for CPU profiling instead of CLI flags
Consolidate CPU profiling to use the inspector-based approach in
cpu-profile.ts instead of injecting --cpu-prof CLI flags:
- Enhance cpu-profile.ts to support NEXT_CPU_PROF_DIR for output path
- Remove redundant --cpu-prof flag injection from next-dev.ts
- Update profiling script to use NEXT_CPU_PROF env var
The inspector API is cleaner and doesn't require modifying execArgv
for forked processes.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>