Update test suite to support pytest-xdist

The unittest suite has grown extensively and especially the TUI snapshot tests are taking up a significant portion of the runtime. Almost all of those are theoretically parallelizable through pytest-xdist but the stateful setup of many unittests prevents this from being used in practice.

We should revisit the test setup to avoid clashing on the same temporary state locations to support leveraging pytest-xdist to speed up the overall runtime of the test suite.