Notably git-cmd which comes with git installations on Windows alters the
encoding resulting in CPython tracing encodings/cp1252.py calls.

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.

Signed-off-by: Damien George <damien@micropython.org>

This is consistent with the other 'micro' modules and allows implementing
additional features in Python via e.g. micropython-lib's sys.

Note this is a breaking change (not backwards compatible) for ports which
do not enable weak links, as "import sys" must now be replaced with
"import usys".

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.

With this patch exceptions that are re-raised have improved tracebacks
(less confusing, match CPython), and it makes re-raise slightly more
efficient (in time and RAM) because they no longer need to add a traceback.
Also general VM performance is not measurably affected.

Partially fixes issue #2928.

With this patch exception tracebacks that go through a finally are improved
(less confusing, match CPython), and it makes finally's slightly more
efficient (in time and RAM) because they no longer need to add a traceback.

Partially fixes issue #2928.