Mounting a bdev directly tries to auto-detect the filesystem and if none is
found an OSError(19,) should be raised.
The fourth parameter of readblocks() and writeblocks() must be optional to
support ports with MICROPY_VFS_FAT=1. Otherwise mounting a bdev may fail
because looking for a FATFS will call readblocks() with only 3 parameters.
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.
