Add controller-level tests for timezone handling in Query

[ukutaht]

From conversations with @aerosol we probably want to refactor Query internals to use NaiveDateTime so we don't carry around useless and confusing timezone information in the Query datetimes.

This PR adds some tests that give guardrails and increase confidence in timezone behaviour that is observable to clients:

• Relative date handling: today should be the current day in the site's timezone, not utc. Previously untested.
• Ambigous and gap handling in timezone conversions: Currently tested via unit tests internally which also use DateTime over Naive. Doesn't give much confidence for refactoring. New controller-level tests only test observable behaviour, not internals, helping much more with refactoring.
• Legacy time on page cutoff: the cutoff is shifted to site timezone with ambigous/gap handling. I don't know if this is really necessary, a couple hours here or there with the cutoff should not have noticeable effects on data. We could move this to Naive and ignore any timezones in cutoff handling. But I wanted to cover this behaviour with tests so we can be intentional about it in refactoring.

[aerosol]

Nice one! I admit I haven't checked if the comments are true though 😅

[ukutaht]

Nice one! I admit I haven't checked if the comments are true though 😅

Fair, but I've verified that each test has a corresponding piece of production code that will cause the test to fail if the implementation changes. So we know that the tests are actually testing something :)

[aerosol]

I'll merge since it fell out of the queue