Should we error when passing duplicate keys to select-*, etc.?

[camsaul]

Apparently this used to work, completely unintentionally, in Toucan 1:

(db/select-field :category_id Venue
                 :category_id [:in allowed-category-ids]
                 :category_id [:not-in disallowed-category-ids])

That was never intentional. I don't think supporting this is really worth it in terms of making the library more complicated and having even more things that need to be documented, but it would be nice to error in this case to prevent people from accidentally trying to do something like this anyway.

This should also be documented in the "differences from Toucan 1" documentation.