Improve typing for WithXPermissions fixtures

[matthewelwell]

The types defined here are not valid according to mypy. Currently, all usages of the functions returned by these fixtures raise the following error in mypy's type checking:

error: Too few arguments  [call-arg]

I have already tried moving to using a Protocol definition like the following:

class WithEnvironmentPermissionsCallable(Protocol):
    def __call__(
        self,
        permission_keys: Optional[list[str]] = None,
        environment_id: Optional[int] = None,
        admin: bool = False,
    ) -> UserEnvironmentPermission: ...

However, this just results in a different error:

error: Incompatible return value type (got "Callable[[list[str] | None, int | None, bool], UserEnvironmentPermission]", expected "WithEnvironmentPermissionsCallable")  [return-value]
note: "WithEnvironmentPermissionsCallable.__call__" has type "Callable[[DefaultArg(list[str] | None, 'permission_keys'), DefaultArg(int | None, 'environment_id'), DefaultArg(bool | None, 'admin')], UserEnvironmentPermission]"

[matthewelwell]

One option here would be to go with the protocol above as this will allow us to remove the type: ignores on each of the uses of the fixtures, and just add a single ignore on the return statement of the fixture (e.g. here). A similar option would be to use cast on the return to force mypy to believe it's correct.

Both of these feel like workarounds though so I'm keen to find a better approach.