[ruff] Implement unnecessary-nested-literal (RUF041)

[sbrugman]

Summary

Implementing unnecessary-nested-literal.

This rule could help simplify other rules' fixes by handling the flattening of Literals here.

See also https://github.com/astral-sh/ruff/pull/14270/files#r1837810594 (unions in a follow-up PR)

Test Plan

cargo test

The ecosystem results are correct.

Some of the nesting emits multiple violations.
I've got a fix for this, but that depends on #14280.
We can go on with merging this PR after review regardless (the violations are not wrong).

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

ℹ️ ecosystem check detected linter changes. (+3 -0 violations, +0 -0 fixes in 2 projects; 53 projects unchanged)

DisnakeDev/disnake (+2 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

+ tests/test_utils.py:730:18: RUF041 [*] Unnecessary nested `Literal`
+ tests/test_utils.py:758:10: RUF041 [*] Unnecessary nested `Literal`

python/typeshed (+1 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview --select E,F,FA,I,PYI,RUF,UP,W

+ stdlib/xml/dom/pulldom.pyi:23:131: E501 Line too long (153 > 130)

Changes by rule (2 rules affected)

code	total	+ violation	- violation	+ fix	- fix
RUF041	2	2	0	0	0
E501	1	1	0	0	0

[MichaReiser]

@AlexWaygood would you mind doing a quick glance at the rule definition? I already reviewed the code

[AlexWaygood]

Similar to #14319 (review), I feel like I'm not sure how much this antipattern really comes up in practice. But, I can see the value if this is a pattern that could be introduced by the fix for other rules we implement!

[MichaReiser]

Is there any open feedback that needs addressing? I'm otherwise happy to merge this rule.

[AlexWaygood]

My feedback has been addressed, but it looks like there's quite a few merge conflicts here. The conversations in #14323 (comment) and #14323 (comment) are also not marked as "resolved", and I think you're better placed to judge whether they should be or not ;)