🐛 Allow type_ kwarg in sa_column_kwargs

[RobertRosca]

In #156 @phi-friday wanted to pass sa_column_kwargs={"type_": Unicode} to a Field to set the column to nvarchar, doing this causes an exception:

File "/usr/local/lib/python3.9/site-packages/sqlalchemy/sql/schema.py", line 1586, in __init__
raise exc.ArgumentError(
sqlalchemy.exc.ArgumentError: May not pass type_ positionally and as a keyword.

sa_type is passed by get_column_from_field as a positional argument, so passing it through at a kwarg leads to this exception.

PR checks if type_ is in the kwargs, and if it is it pops it from the kwargs and sets sa_type to its value.

Also added a test for this case, @tiangolo is issue-related tests in a separate directory a thing you like? It's not done in FastAPI or here, so if not I'll move it.

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Edit: whoops, forgot the sa_column argument existed, given that this seems kind of pointless 🤔

[tiangolo]

Thanks @RobertRosca! SQLAlchemy only allows types in the sequential arguments, not in keyword arguments. So it would have been in sa_column_args. But still, probably more control in sa_column.

Either way, there's now support for sa_type which should simplify it: #505

That will be available in 0.0.11. 🎉

Given that, I'll close this one, thanks for the effort! ☕