docs: Extend CONTRIBUTING.md with code guidelines

[jlaportebot]

Summary

Extends CONTRIBUTING.md with comprehensive code guidelines for contributors, including:

• Code style and formatting standards
• Testing requirements and patterns
• Documentation expectations
• Commit message conventions
• Code review guidelines

Addresses feedback from maintainers on the initial submission.

Changes

• Added detailed code guidelines section
• Clarified testing expectations
• Documented commit message format
• Added code review checklist

[alexandear]

@jlaportebot Why was the previous PR #4202 closed? It has a lot of useful comments.

[alexandear]

@gmlewis I think updating the CONTRIBUTING.md should be done either by a maintainer (you), a reviewer, or any contributor with a significant number of merged commits into the library — e.g., the top 15 from the graph.

[gmlewis]

@gmlewis I think updating the CONTRIBUTING.md should be done either by a maintainer (you), a reviewer, or any contributor with a significant number of merged commits into the library — e.g., the top 15 from the graph.

So I'm of the opinion (derived from empirical evidence) that most contributors do not bother to read CONTRIBUTING.md, unfortunately. I'm also of the opinion that one of the reasons might be "TL;DR" (it is too enormous).

I understand the arguments about making it super detailed, accounting for as many scenarios as possible that a contributor might encounter while writing a PR so that an AI Agent can slurp it all in and do a better job, but at the same time I don't want to drive away humans from contributing just because it appears to be a daunting experience before they even get started.

Therefore, if one of our esteemed and greatly appreciated REVIEWERS wishes to improve it, that sounds wonderful to me. If others see gaps that they feel need filling, I think it is fine for we, as fellow contributors, to review and incorporate if we feel there is value.

I hope this makes sense.