Vec2d: type hints for add/sub reject Vec2d despite docstrings

```
from pymunk import Vec2d

a = Vec2d(0, 0)
b = Vec2d(0, 1)

c = a + b
```
`
Expected type 'tuple[float, float]', got 'Vec2d' instead 
`

`vec2d.py`
```
...
"""Add a Vec2d with another Vec2d or tuple of size 2.
...
def __add__(self, other: tuple[float, float]) -> "Vec2d":
...
```