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/float/builtin_float_abs.py

@@ -1,13 +1,13 @@
 # test builtin abs function with float args
 
 for val in (
-    '1.0',
-    '-1.0',
-    '0.0',
-    '-0.0',
-    'nan',
-    '-nan',
-    'inf',
-    '-inf',
-    ):
+    "1.0",
+    "-1.0",
+    "0.0",
+    "-0.0",
+    "nan",
+    "-nan",
+    "inf",
+    "-inf",
+):
     print(val, abs(float(val)))