Dialect: Add support for `asyncpg` and `psycopg3` drivers

[amotl]

About

This patch adds support for asyncpg and psycopg3 drivers, by introducing the crate+asyncpg:// and crate+psycopg:// dialect identifiers.

It also adds the crate+urllib3:// dialect identifier, for explicitly addressing the urllib3-based transport, in case there might be other HTTP-based transport adapters in the future, using libraries like aiohttp, httpx, or niquests. [^1]

Notes

• The asynchronous variant of psycopg is also supported and will be automatically selected when using create_async_engine() instead of create_engine(), so it doesn't have a dedicated dialect identifier.

• All of this will only work with SQLAlchemy 2.x.

Installation

pip install 'sqlalchemy-cratedb[all] @ git+https://github.com/crate/sqlalchemy-cratedb@amo/postgresql-async'

References

• https://github.com/crate/sqlalchemy-cratedb/issues/80
• https://github.com/crate/sqlalchemy-cratedb/issues/79
• https://github.com/crate/sqlalchemy-cratedb/issues/74
• https://github.com/crate/crate-python/pull/532

Backlog

• [ ] Address bug with psycopg, see below.
• [ ] Documentation.
• [x] Software tests.
• [x] Code examples. See https://github.com/crate/cratedb-examples/pull/201.

[^1]: Picked up from another discussion at https://github.com/panodata/grafana-client/issues/134.