[flake8-class-newline] Add new flake8 plugin.

[augustelalande]

Summary

Add new flake8 plugin, flake8-class-newline which enforces a single blank line between a class definition and its first method.

Test Plan

Test cases have been added.

[augustelalande]

I don't really understand the compiling issue, in the test failure.

[MichaReiser]

I think we should exclude pyi files from this rule because empty lines in stub files should only be used for grouping methods.

[augustelalande]

Done

[codspeed-hq]

CodSpeed Performance Report

Merging #10033 will degrade performances by 4.04%

_{Comparing augustelalande:class_newline (4282d15) with main (8dc22d5)}

Summary

❌ 1 regressions
✅ 29 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	main	augustelalande:class_newline	Change
❌	linter/default-rules[large/dataset.py]	19.1 ms	19.9 ms	-4.04%

[MichaReiser]

Thanks.

I took another look at the rule and, unfortunately, it is incompatible with our formatter that always removes empty lines between the class header and the first method.

Ruff doesn't have a good model to support formatter incompatible rules. The problem is that users using --select ALL automatically opt in to the rule, and there's a good number of people using ALL. We plan to resolve this by categorizing the rules. But we can't merge this rule until we figured the categorization out. I'm sorry

[augustelalande]

Ok no worries, appreciate the time. Should I close this PR, or keep it open for now?