The original logic of reducing a full path to a relative one assumes
"tests/misc" is in the filename which is limited in usage: it never works
for CPython on Windows since that will use a backslash as path separator,
and also won't work when the filename is a path not relative to the tests
directory which happens for example in the common case of running
"./run-tests -d misc".

Fix all cases by printing only the bare filename, which requires them all
to start with sys_settrace_ hence the renaming.

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.