Support Struct columns

[adriangb]

What should we do with these? Custom types in Postgres are messy because we need to know (1) the name to emit DDL and (2) the OIDs of the inner types, which is messy when dealing with nested types like arrays. Maybe we should copy these over as JSONB?

[adriangb]

So I think the thing to do here is ask the user to get the OIDs for us:

needed_metadata = analyze_metadata(schema)

metada = await some_util_funcion_per_db_driver(needed_metada, some_connection)

encoder = Encoder(schema, metadata)

The key is that the rust package remain sans-io and with no dependency on a particular database driver (which would make it much harder to be language agnostic).

[adriangb]

Making progress here. We can now specify the encoder to use for each column. We just need the utility function.