Added support to add an interval to a timestamp

[jorgecarleitao]

This adds support for adding an interval to a timestamp with timezone, thus taking leap days (Feb 29th) and leap hours (daylight saving) into account.

This brings the last missing piece to fully support timestamps with timezones: we can now convert them from and to strings, and perform basic interval arithmetic taking the timezone into account.

3 examples:

• adding 1 hour to 2020-03-29 00:00:00 WET results in 2020-03-29 02:00:00 WEST
• adding 7 months and 1 hour to 2020-03-29 00:00:00 WET results in 2020-10-29 01:00:00 WET

the former crosses one summer time shift (and thus adds an extra hour), the latter crosses both (and thus adds no extra hour).

• adding 1d,1h,1m to 1972-02-28 01:00:00 +01:00 results in 1972-02-29 02:01:00 +01:00

because 1972 has a leap year.

When the timestamp has no timezone information, days are 24 * 60 * 60.

Closes #23

[codecov]

Codecov Report

Merging #417 (bdb6856) into main (d5cc0db) will decrease coverage by 0.08%.
The diff coverage is 56.15%.

@@            Coverage Diff             @@
##             main     #417      +/-   ##
==========================================
- Coverage   80.96%   80.88%   -0.09%     
==========================================
  Files         347      347              
  Lines       22201    22276      +75     
==========================================
+ Hits        17976    18018      +42     
- Misses       4225     4258      +33     

Impacted Files	Coverage Δ
src/compute/cast/primitive_to.rs	83.67% <0.00%> (+1.12%)	⬆️
src/compute/arithmetics/time.rs	87.78% <15.38%> (-9.71%)	⬇️
src/compute/arithmetics/mod.rs	49.64% <16.66%> (-1.49%)	⬇️
src/compute/temporal.rs	85.98% <50.00%> (+2.19%)	⬆️
src/temporal_conversions.rs	75.35% <53.06%> (-8.81%)	⬇️
src/array/display.rs	61.15% <72.72%> (-0.55%)	⬇️
tests/it/temporal_conversions.rs	100.00% <100.00%> (ø)
src/types/mod.rs	29.20% <0.00%> (+0.88%)	⬆️

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[jorgecarleitao]

cc @sundy-li @ritchie46 since I saw you both working with interval arithmetics recently ^_^