B901 catches yields in subexprs and more sensitive B901

[guptaarnav]

Summary

Closes #14453 by updating the implementation of the B901 lint rule. The changes ensure that:
1. The visitor now traverses all expressions within statements, ensuring yield expressions embedded are correctly flagged even if they are not the expression of an ExprStmt.
2. The rule now correctly identifies yield and yield from expressions when they appear as the right-hand side of assignment statements (e.g., x = yield or x = yield from []); this catches the case mentioned in the original issue by @AlexWaygood.
3. We still do not recurse into lambda expressions or nested function defs as these are evaluated separately.

Test Plan

I added the tests mentioned by @MichaReiser and @AlexWaygood in the original issue into test/fixtures/flake8_bugbear/B901.py and updated the related snapshot.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

ℹ️ ecosystem check detected linter changes. (+32 -0 violations, +0 -0 fixes in 2 projects; 53 projects unchanged)

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

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

+ src/trio/_core/_traps.py:63:5: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior

pytest-dev/pytest (+31 -0 violations, +0 -0 fixes)

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

+ src/_pytest/assertion/__init__.py:188:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/cacheprovider.py:298:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/cacheprovider.py:419:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/cacheprovider.py:461:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/capture.py:872:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/capture.py:877:13: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/capture.py:882:13: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/capture.py:887:13: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/config/__init__.py:1435:13: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/debugging.py:303:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/faulthandler.py:88:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/helpconfig.py:133:5: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/logging.py:780:17: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/logging.py:788:17: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/logging.py:801:17: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/logging.py:869:17: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/pytester.py:171:13: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/setuponly.py:36:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/skipping.py:257:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/skipping.py:292:5: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/terminal.py:683:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/terminal.py:914:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/terminal.py:925:13: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/tmpdir.py:313:5: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/unittest.py:428:5: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/warnings.py:110:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/warnings.py:119:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/warnings.py:129:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/warnings.py:90:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ src/_pytest/warnings.py:99:9: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior
+ testing/conftest.py:89:5: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
B901	32	32	0	0	0

[guptaarnav]

Saw a large number of violations from the automated ruff-ecosystem check. primarily seems to be from code that says return (yield) which is valid. rethinking this PR, closing for now.