[red-knot] @override lint rule (#11282)
## Summary
Lots of TODOs and things to clean up here, but it demonstrates the
working lint rule.
## Test Plan
```
➜ cat main.py
from typing import override
from base import B
class C(B):
@override
def method(self): pass
➜ cat base.py
class B: pass
➜ cat typing.py
def override(func):
return func
```
(We provide our own `typing.py` since we don't have typeshed vendored or
type stub support yet.)
```
➜ ./target/debug/red_knot main.py
...
1 0.012086s TRACE red_knot Main Loop: Tick
[crates/red_knot/src/main.rs:157:21] diagnostics = [
"Method C.method is decorated with `typing.override` but does not override any base class method",
]
```
If we add `def method(self): pass` to class `B` in `base.py` and run
red_knot again, there is no lint error.
---------
Co-authored-by: Micha Reiser <micha@reiser.io>
