feat: exclude warmup rounds from perf flamegraph

[not-matthias]

No description provided.

[Copilot]

Pull request overview

This PR aims to prevent warmup-only forks from polluting CodSpeed/perf flamegraphs by marking warmup forks at JVM startup and suppressing benchmark marker emission in those forks.

Changes:

• Add a warmup-fork flag to forked JVM command construction and propagate it via a system property.
• Suppress CodSpeed benchmark marker emission in forked JVMs identified as warmup-only forks.
• Update tests for the changed getForkedMainCommand signature and exclude native-* directories from the license plugin.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
jmh-fork/jmh-core/src/test/java/org/openjdk/jmh/runner/RunnerTest.java	Updates test calls to the new getForkedMainCommand(..., warmupFork) signature.
jmh-fork/jmh-core/src/main/java/org/openjdk/jmh/runner/Runner.java	Passes warmupFork to fork command builder and adds -Dio.codspeed.warmupFork=true for warmup forks.
jmh-fork/jmh-core/src/main/java/org/openjdk/jmh/runner/BaseRunner.java	Introduces warmup-fork detection and attempts to add benchmark start/end markers for measurement iterations (suppressed for warmup forks).
jmh-fork/jmh-core/pom.xml	Excludes native-*/** from the license formatting/check plugin.

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[codspeed-hq]

Merging this PR will degrade performance by 20.31%

❌ 2 regressed benchmarks
✅ 123 untouched benchmarks
⏩ 9 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	fibonacciBottomUp[20]	1.2 µs	1.4 µs	-12.92%
❌	dualPivotQuickSort[10000]	4.9 ms	6.1 ms	-20.31%

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_{Comparing cod-2528-exclude-warmup-rounds-from-perf-flamegraph-in-java (ff83f3b) with main (c7c19aa)}

Footnotes

1. 9 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩