Remove embedded Cassandra integration test mode in favor of Testcontainers

[mp911de]

Compatibility verified. Upgrading cassandra-all to 4.0.0 requires a few changes and pretty often the server doesn't come up properly. Requires follow-up in a separate ticket.

Originally posted by @mp911de in #1123 (comment)

[mp911de]

Testcontainers have proved to be reliable and creating less hassle than upgrading regularly cassandra-all with all the involved dependency hygiene dance.