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.
New keyword option in constructor and init() method is "dma=<bool>".
DMA is now disabled by default for I2C transfers because it currently does
not handle I2C bus errors very well (eg if slave device doesn't ACK or
NACK correctly during a transfer).
