gigasecond-anniversary: solving in web editor and time zone

It seems like the test runner uses UTC as the system time zone.

I first solved this online without providing the time-zone argument for either encode-universal-time or decode-universal-time.

Then I downloaded locally and was surprised by the test failures. I learned about the importance of the time-zone arguments and updated my solution.

I suppose there are consequences to setting the system timezone of the test runner's Docker container to a non-UTC timezone (perhaps reporting, ...). Would it be possible for the test-runner to detect the slug represents a "date-time" exercise and set the TZ env var to something else?

This is probably more of a common-lisp-test-runner issue I suppose...