Fixed casting of utf8 <> Timestamp with and without timezone

[jorgecarleitao]

This PR fixes multiple errors in cast timestamps with timezones to and from utf8. It also systematizes the rules.

This PR adds a new optional dependency, chrono-tz, that is used for calculations with timezones other than "+WX:YZ" and "UTC". Those timezones have offsets that vary in time (e.g. DST), which chrono-tz solves. When the feature is not active and the timezone is e.g. "London", the cast errors.

Utf8 in RFC3339 <-> Timestamp with timezone

These casts are lossless. Strings with different timezones are mapped accordingly to the target timezone via offsets (handled by chrono and chrono-tz).

Utf8 without timezone -> Timestamp with timezone

These casts result in nulls (on an element-by-element basis). There is no unique way of converting these. Users need to perform two casts to add a timezone to a string without a timezone: Utf8 -> Timestamp(_, None) -> Timestamp(_, Some(tz)), where the latter is O(1) and is where the user is explicit about the assumption that the time is in that timezone.

Utf8 -> Timestamp without timezone

These casts are null iff the string is not in RFC3339. Other formats should be handled by temporal_conversions::utf8_to_timestamp_ns and temporal_conversions::utf8_to_naive_timestamp_ns, whose one of the arguments is the format (e.g. "%Y-%m-%dT%H:%M:%S%.f%:z" for RFC3339).

Timestamp without timezone -> Utf8

It is printed in the ISO 8601 format without timezone information (e.g. 1996-12-19 16:39:57), which is the display offered by chrono::NaiveDateTime.

Displaying timestamps follows the same rules as timestamp -> utf8

Overall, this offers a more controlled environment over timezones.

[codecov]

Codecov Report

Merging #376 (7663978) into main (3af5ffe) will decrease coverage by 0.03%.
The diff coverage is 81.53%.

@@            Coverage Diff             @@
##             main     #376      +/-   ##
==========================================
- Coverage   81.18%   81.15%   -0.04%     
==========================================
  Files         330      330              
  Lines       21823    21915      +92     
==========================================
+ Hits        17717    17785      +68     
- Misses       4106     4130      +24     

Impacted Files	Coverage Δ
src/compute/cast/primitive_to.rs	82.55% <53.57%> (-17.45%)	⬇️
src/temporal_conversions.rs	82.17% <82.97%> (+6.79%)	⬆️
src/compute/cast/mod.rs	88.67% <91.66%> (+<0.01%)	⬆️
src/compute/cast/utf8_to.rs	92.98% <100.00%> (+0.38%)	⬆️
tests/it/compute/cast.rs	99.30% <100.00%> (+0.07%)	⬆️
tests/it/temporal_conversions.rs	100.00% <100.00%> (ø)
src/io/json_integration/write.rs	6.25% <0.00%> (+6.25%)	⬆️

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