Expand docs for ASYNC109

[jamesbraza]

Summary

Documenting when to use or not use ASYNC109 a bit more.

Closes #12353

Test Plan

It wasn't tested

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[AlexWaygood]

Thanks! I agree the docs for this function can be improved, and I think this is a step in the right direction overall. However, I'm not sure the PR fully addresses @jakkdl's comments in #12353 (comment) and #12353 (comment). It would be great if the rule's docs could attempt to give a proper explanation of why the rule exists in the first place (to help enforce opinionated design decisions relating to a broader philosophy of how structured concurrency works), probably linking to https://vorpus.org/blog/some-thoughts-on-asynchronous-api-design-in-a-post-asyncawait-world/#timeouts-and-cancellation.

I guess those updates don't necessarily need to be made in this PR, but I don't think this PR is sufficient to close out #12353 as it currently stands

[jamesbraza]

Alright, I just added a small blurb mentioning structured concurrency and linking that blog post 👌

Thanks for the detailed and thoughtful review

[AlexWaygood]

Thanks!

[codspeed-hq]

CodSpeed Performance Report

Merging #13146 will degrade performances by 5.48%

_{Comparing jamesbraza:better-async109-docs (7f61ec7) with main (52d8847)}

Summary

❌ 1 regressions
✅ 31 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	main	jamesbraza:better-async109-docs	Change
❌	linter/all-rules[numpy/globals.py]	727.5 µs	769.7 µs	-5.48%