Add RUF072: warn when using operator on an f-string (#24162)
## Summary
Fixes #24159
Adds a new rule RUF072 (`fstring-percent-format`) that flags any use of
the `%` operator on an f-string.
Mixing f-string interpolation with `%`-formatting is almost certainly a
mistake since both serve the same purpose. There's no valid use case for
using `%` on an f-string.
```python
# Flagged
f"{name}" % name
f"hello %s %s" % (1, 2)
f"value: {x}" % {"key": "value"}
# OK — plain string literals are handled by existing F50x rules
"hello %s" % name
"%s %s" % (1, 2)
```
## Test Plan
- Added test cases for f-strings with `%` on various RHS types
(variables, tuples, dicts, literals)
- Added test cases for plain string literals (not flagged — handled by
F50x)
- Verified existing ruff and pyflakes tests still pass
```shell
cargo test -p ruff_linter -- fstring_percent_format
```
Test file:
`crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__RUF072_RUF072.py.snap`
Test cases cover:
- F-string with `%` and variable RHS: `f"{banana}" % banana`
- F-string with `%` and tuple RHS: `f"hello %s %s" % (1, 2)`
- F-string with `%` and dict RHS: `f"value: {x}" % {"key": "value"}`
- F-string with `%` and literal RHS: `f"{x}" % 42`
- Plain string literals not flagged (handled by existing F50x rules)
