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/stress_create.py

@@ -6,9 +6,11 @@ except ImportError:
     import time
 import _thread
 
+
 def thread_entry(n):
     pass
 
+
 thread_num = 0
 while thread_num < 500:
     try:
@@ -19,4 +21,4 @@ while thread_num < 500:
 
 # wait for the last threads to terminate
 time.sleep(1)
-print('done')
+print("done")