## Summary
Per the suggestion in
https://github.com/astral-sh/ruff/discussions/6183, this PR removes
`AsyncWith`, `AsyncFor`, and `AsyncFunctionDef`, replacing them with an
`is_async` field on the non-async variants of those structs. Unlike an
interpreter, we _generally_ have identical handling for these nodes, so
separating them into distinct variants adds complexity from which we
don't really benefit. This can be seen below, where we get to remove a
_ton_ of code related to adding generic `Any*` wrappers, and a ton of
duplicate branches for these cases.
## Test Plan
`cargo test` is unchanged, apart from parser snapshots.
## Summary
The `SemanticModel` currently stores the "body" of a given `Suite`,
along with the current statement index. This is used to support "next
sibling" queries, but we only use this in exactly one place -- the rule
that simplifies constructs like this to `any` or `all`:
```python
for x in y:
if x == 0:
return True
return False
```
Instead of tracking the state, we can just do a (slightly more
expensive) traversal, by finding the node within its parent and
returning the next node in the body.
Note that we'll only have to do this extremely rarely -- namely, for
functions that contain something like:
```python
for x in y:
if x == 0:
return True
```
