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.
This commit adds micropython.heap_locked() which returns the current
lock-depth of the heap, and can be used by Python code to check if the heap
is locked or not. This new function is configured via
MICROPY_PY_MICROPYTHON_HEAP_LOCKED and is disabled by default.
This commit also changes the return value of micropython.heap_unlock() so
it returns the current lock-depth as well.
This test for calling gc_realloc() while the GC is locked can be done in
pure Python, so better to do it that way since it can then be tested on
more ports.
