I have the following model

```py
class Window(BaseModel):
    size: tuple[int, int]

```

and I would like to instantiate it like this:

```py
fields = {'size': '1920x1080'}
window = Window(**fields)

```

Of course this fails since the value of `'size'` is not of the correct type. However, I would like to add logic so that the value is split at `x`, i.e.:

```py
def transform(raw: str) -> tuple[int, int]:
    x, y = raw.split('x')
    return int(x), int(y)

```

Does Pydantic support this?