## Summary
The motivation here is that it will make this rule easier to rewrite as
a deferred check. Right now, we can't run this rule in the deferred
phase, because it depends on the `except_handler` to power its autofix.
Instead of lexing the `except_handler`, we can use the `SimpleTokenizer`
from the formatter, and just lex forwards and backwards.
For context, this rule detects the unused `e` in:
```python
try:
pass
except ValueError as e:
pass
```
## Summary
We have two `Cursor` implementations. This PR moves the implementation
from the formatter into `ruff_python_whitespace` (kind of a poorly-named
crate now) and uses it for both use-cases.
## Summary
We use `.trim()` and friends in a bunch of places, to strip whitespace
from source code. However, not all Unicode whitespace characters are
considered "whitespace" in Python, which only supports the standard
space, tab, and form-feed characters.
This PR audits our usages of `.trim()`, `.trim_start()`, `.trim_end()`,
and `char::is_whitespace`, and replaces them as appropriate with a new
`.trim_whitespace()` analogues, powered by a `PythonWhitespace` trait.
In general, the only place that should continue to use `.trim()` is
content within docstrings, which don't need to adhere to Python's
semantic definitions of whitespace.
Closes#4991.
## Summary
`ruff_newlines` becomes `ruff_python_whitespace`, and includes the
existing "universal newline" handlers alongside the Python
whitespace-specific utilities.
