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/internal_bench/arrayop-2-list_map.py

@@ -4,9 +4,11 @@
 # array). On the other hand, input array stays intact.
 import bench
 
+
 def test(num):
-    for i in iter(range(num//10000)):
+    for i in iter(range(num // 10000)):
         arr = [0] * 1000
         arr2 = list(map(lambda x: x + 1, arr))
 
+
 bench.run(test)