tests for succesfull avro "compilation"

[untzag]

Unfortunately, one of the more common bugs we have experienced is successfully processing <kind>.avpr, config.toml and state.toml using fastavro. This is especially relevant when dealing with complex named data types defined by individual daemons.

We should refactor yaqd-core internals to make it easy to run this processing outside of daemon instantiation. We can then write unit tests which verify that processing works properly and ensure that this type of bug never hits us again in production.