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.
Fixes UDP non-blocking recv so it returns EAGAIN instead of ETIMEDOUT.
Timeout waiting for incoming data is also improved by replacing 100ms delay
with poll_sockets(), as is done in other parts of this module.
Fixes issue #5759.