document how to do good performance work

[sylvestre]

No description provided.

[Copilot]

Pull Request Overview

This PR adds a new documentation page that explains how to profile and benchmark performance improvements using tools like Hyperfine and Samply. Key changes include:

• A step-by-step tutorial on setting up performance benchmarks.
• Example commands for both benchmarking with Hyperfine and profiling with Samply.
• A workflow outlining the process from baseline measurement to verifying improvements.

Comments suppressed due to low confidence (1)

docs/src/performance.md:7

• [nitpick] Consider using consistent list formatting for the benchmarking steps outlined in this section. For instance, using numbered lists consistently rather than mixing numbered steps (lines 11-13) with bullet points (lines 16-17) could improve clarity.

### Benchmarking Best Practices

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[cakebaker]

Good work :)