Replace `integration-tests` module with conventional rust integs in their relevant modules

[jcrossley3]

The fundamental module seemed appropriate for most of the integs.

This moves all the integ-specific test data to etc/test-data with the rest of it, and relies on the TrustifyContext instance passed to each test to find it, whether bytes or stream, and/or ingest it for the test.

This removed some redundancy from the integs (e.g. streams, xz) in light of recent features added to TrustifyContext.

[bobmcwhirter]

Thanks for this!