Nested custom types in Postgres break `asyncpg.Record` subclassing

• asyncpg version: v0.25.0

• PostgreSQL version: 14

• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: on-premise

• Python version: 3.10.1

• Platform: linux

• Do you use pgbouncer?: no

• Did you install asyncpg with pip?: yes

• If you built asyncpg locally, which version of Cython did you use?: n/a

• Can the issue be reproduced under both asyncio and
  uvloop?: n/a

It would appear that nested types are not converted to a user specified record_class, and instead will always use asyncpg.Record.

For example:

CREATE TYPE my_custom_type AS (
    id int,
    filename text,
    sql text
);

CREATE TABLE my_table (
    files my_custom_type[] NOT NULL,
);

SELECT * FROM my_table

If you specify a custom record_class, then the record from SELECT * FROM my_table will be your subclass. However, the value inside record['files'] will use the asyncpg.Record class, rather than the custom one specified.

What should actually happen?

I think if a user specifies a record_class, then this class should always be used, even for nested custom types. It's quite unexpected behaviour for asyncpg to use the default class when a custom one has been specified.

Start by reproducing the issue with the custom PostgreSQL type, array column, SELECT query, and a custom record_class described in the report. Trace how nested custom-type values are decoded and how record_class is propagated; done means records inside record['files'] use the specified subclass rather than asyncpg.Record, with regression coverage for this case.