This adds the Python files in the tests/ directory to be formatted with
./tools/codeformat.py. The basics/ subdirectory is excluded for now so we
aren't changing too much at once.
In a few places `# fmt: off`/`# fmt: on` was used where the code had
special formatting for readability or where the test was actually testing
the specific formatting.
Depending on the thread scheduler, a busy-wait loop can hog the CPU and
make the tests very slow. So convert such loops to loops that have an
explicit sleep, allowing the worker threads to do their job.
