tests: Format all Python code with black, except tests in basics subdir.

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.

tests/thread/thread_exc2.py

@@ -2,9 +2,11 @@
 import utime
 import _thread
 
+
 def thread_entry():
     raise ValueError
 
+
 _thread.start_new_thread(thread_entry, ())
 utime.sleep(1)
-print('done')
+print("done")