feat: add typings for functions returning table

[jsbrain]

What kind of change does this PR introduce?

Fixes #468

[soedirgo]

Hey, thanks! There's actually a bug in return_type - I'll fix that and then come back to this PR.

[jsbrain]

Yeah I also realized meanwhile that my code doesn't work reliably. If you have 2 tables with the same name in 2 different schemas you would have the chance to get the typings of the wrong table in the "other" schema.

For this to work properly there would have to be more information in the return_type, like public.users instead of users or there might be another way to infer this correctly but I'm not sure.

[soedirgo]

Yep, the plan is to add a return_type_id field, so we can disambiguate which table is referred exactly.

[jsbrain]

Sounds like a plan 👍🏻

[soedirgo]

Closing in favor of #500