Add Test Execution Documentation and Windows Helper Script

[mamaorha]

This content was initially generated with AI assistance (Copilot), but I believe it provides important guidance for developers. It helps explain how to set up and run the test suite and outlines the considerations required for testing on Windows.

At the moment, developers often need to reverse-engineer the CI pipeline to understand the required steps and environment. The goal of this documentation is to make that process more transparent, reduce onboarding friction, and provide a clear, reliable reference for local test execution and Windows-specific testing workflows.

[codspeed]

Merging this PR will not alter performance

✅ 28 untouched benchmarks

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_{Comparing mamaorha:docs (e534dc3) with main (35b0dc9)¹}

Footnotes

1. No successful run was found on main (8de3833) during the generation of this report, so 35b0dc9 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩