check for overlapping overloads

pyright's `reportOverlappingOverload` rule checks for this:

```py
from typing import overload

@overload
def foo(value: object) -> object: ...
@overload
def foo(value: int) -> int: ... # Overload 2 for "foo" will never be used because its parameters overlap overload 1 (reportOverlappingOverload)

def foo(value: object) -> object: ...
```