Add integration tests

[mikn]

This should include concurrency tests to make sure that there are no race conditions and ensure that high-contention doesn't result in race conditions. Would also be beneficial to have comparative benchmarks under these circumstances, but not necessary.

[mikn]

I think the easiest path forward for this would be to just add the benchmarks with an integration test setup using Github Actions and then follow up with more comprehensive integration tests for the rest of the library afterwards.