Get Avro testing working in fully automated fashion

[jeff303]

Currently, the Avro test requires running docker compose outside of Clojure, then using a fixture to bind the corresponding vars. Of course, this is suboptimal.

testcontainers does offer Docker compose support. However, from fairly extensive testing, this does not seem to work properly for the purpose of running the Avro tests. It will require some more debugging and experimentation to get working.