In automated testing, separate unit tests from longer verification tests

At some point we will want to run verification tests that may take a long time. Let's create a structure for that to happen separately from unit tests that are meant to run very quickly.

The issue names no files or tests. Start by inspecting the repository's existing automated and unit-test layout, then determine how long-running verification tests should be separated. Done means the repository has a clear separate structure while quick unit tests remain independently runnable.

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