support adbc APIs in DB-API package

[tswast]

Is your feature request related to a problem? Please describe.

Getting data out of the DB-API can be slow for large results, especially if the desired format is Arrow, as is the case in polars (pola-rs/polars#18547, pola-rs/polars#17326)

Describe the solution you'd like

I'd love if our DB-API provided the custom Python methods described in https://arrow.apache.org/adbc/current/python/quickstart.html, such as fetch_arrow_table(), adbc_ingest(), adbc_get_info(), and adbc_get_table_schema (). See: https://arrow.apache.org/adbc/current/python/api/adbc_driver_manager.html#adbc_driver_manager.dbapi.Connection and https://arrow.apache.org/adbc/current/python/api/adbc_driver_manager.html#adbc_driver_manager.dbapi.Cursor

Describe alternatives you've considered

A (better?) alternative would be for BigQuery to provide a real C/C++ ADBC driver, which could then be automatically usable from the Python adbc_driver_manager package.

Additional context

I'm not expecting fast movement here, as the ADBC standard/community still feels pretty early days but figured it was worth filing for visibility given that polars is integrated with it.