WIP, but main extractor paths seem to work

This adds a possible macro for building JDBC type sources.

Right now just a size annotation, also might need an unsigned one.

Number of types available probably needs to increase. But it seems to build most of the info we would need for a source
The type inference would be screwy in instanciation if I just have T be in the jvm type. I could do either have both the JdbcColumn type and the inner type and it seems good. Or leave this as any and drop the type?