chore: enable fair sched for codspeed

[CPunisher]

Summary

It's seems that the codspeed goes very unstable after #12763, so revert part of it.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull request overview

This PR switches from using the official CodSpeed GitHub Action to a local custom action implementation to enable the --fair-sched=yes flag for Valgrind, aiming to stabilize benchmark results. The change is a partial revert of PR #12763.

Changes:

• Replaces the official CodSpeed action with a local custom action
• Adds fair scheduling support via VALGRIND_FLAGS environment variable
• Uses a forked runner from CPunisher/runner with valgrind configuration support

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 9 comments.

File	Description
.github/workflows/reusable-build-bench.yml	Updates the benchmark workflow to use the new local CodSpeed action instead of the official action
.github/actions/codspeed/action.yaml	Adds a new custom CodSpeed action that installs a forked runner and enables fair scheduling for benchmarks

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[github-actions]

Rsdoctor Bundle Diff Analysis

Found 5 projects in monorepo, 0 projects with changes.

📊 Quick Summary

Project	Total Size	Change
react-10k	5.7 MB	0
react-1k	825.4 KB	0
react-5k	2.7 MB	0
rome	984.2 KB	0
ui-components	2.1 MB	0

Generated by Rsdoctor GitHub Action

[github-actions]

📦 Binary Size-limit

Comparing aba24cb to fix: require.resolve() replaced as require() (#12773) by intellild

🙈 Size remains the same at 47.99MB

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing 01-21-chore/fair-lock (aba24cb) with main (48885c7)}

Summary

✅ 16 untouched benchmarks
⏩ 1 skipped benchmark¹

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩