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.
As the mktime documentation for CPython states: "The earliest date for
which it can generate a time is platform-dependent". In particular on
Windows this depends on the timezone so e.g. for UTC+2 the earliest is 2
hours past midnight January 1970. So change the reference to the earliest
possible, for UTC+14.
