Running dotnet test consumes too much memory

[rmshaffer]

Describe the bug Each unit test does not de-allocate the memory that was allocated during the test. Because we have ~90 tests, running dotnet test eventually consumes over 6 GB of RAM, despite the fact that each test run on its own consumes no more than ~100 MB.

Expected behavior Each unit test should fully de-allocate its memory when it finishes.

Additional context As a temporary workaround for CI, we have implemented #222, which breaks up the test run into multiple invocations of dotnet test. That workaround can be removed once this underlying issue is resolved.