Fix issue 28 tz#33
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…ch#28) `get_flights()` previously returned `time_hour` with airport-local wall clocks implicitly tagged as UTC, while `get_weather()` returned true UTC instants tagged as GMT. The two columns therefore disagreed for any non-UTC origin and the canonical `(origin, time_hour)` join produced no rows. After this change both functions return `time_hour` in the airport's IANA `tzone` (looked up from `get_airports()`), matching `nycflights13`'s convention: flights are forced into the local zone (wall clock preserved, instant corrected) and weather is converted into the local zone (instant preserved, wall clock + year/month/day/hour recomputed). New unit tests in `test-8-time-hour-tz.R` exercise both modes and lock in the cross-table join invariant. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
A POSIXct column carries one `tzone` attribute, so the previous "tag each row with its origin's local tz" approach couldn't actually hold for mixed-origin queries -- `bind_rows` collapses the per-group tzs and the printed display silently lies for the losing rows. Reframe the contract: `get_flights()$time_hour` is the correct UTC instant (BTS wall clocks reinterpreted via each origin's IANA tz), `get_weather()$time_hour` already publishes UTC instants, and the `(origin, time_hour)` join works honestly across any combination of time zones. Also removes the weather-side UTC-boundary bug (querying & filtering on UTC months but then converting to local time pulled in adjacent local months), since weather no longer gets a tz conversion. Tests cover DST crossing within a single airport, round-trip back to local wall clocks, multi-tz row ordering, and empty input. Drops `tibble::` usage in tests (undeclared dependency WARNING) in favour of `dplyr::tibble`. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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