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_shared2.py

@@ -5,9 +5,11 @@
 
 import _thread
 
+
 def foo(lst, i):
     lst[i] += 1
 
+
 def thread_entry(n, lst, idx):
     for i in range(n):
         foo(lst, idx)
@@ -15,6 +17,7 @@ def thread_entry(n, lst, idx):
         global n_finished
         n_finished += 1
 
+
 lock = _thread.allocate_lock()
 n_thread = 2
 n_finished = 0