[`ruff`] Add `unnecessary-assign-before-yield` (`RUF070`) (#23300)
## Summary
Closes #13141
Adds a new rule `unnecessary-assign-before-yield` (`RUF070`) that
detects variable assignments immediately followed by a `yield` (or
`yield from`) of that variable, where the variable is not referenced
anywhere else. This is the `yield` equivalent of `RET504`
(`unnecessary-assign`).
```python
# Before
def gen():
x = 1
yield x
# After
def gen():
yield 1
```
Unlike return, yield does not exit the function, so the rule only triggers when the binding has exactly one reference (the yielditself). The fix is marked as unsafe for the same reason.
## Test Plan
cargo nextest run -p ruff_linter -- RUF070
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Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>
