Manually implement Copy for DateTime if offset is Copy

[pitdicker]

Also extended the test to have the type that implements Offset be Send and Copy while the type for TimeZone is not.

Fixes #1571.

[codecov]

Codecov Report

Attention: Patch coverage is 75.67568% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 91.78%. Comparing base (760eb66) to head (74b371a).

Files	Patch %	Lines
src/datetime/tests.rs	75.67%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1573      +/-   ##
==========================================
- Coverage   91.82%   91.78%   -0.04%     
==========================================
  Files          37       37              
  Lines       18173    18208      +35     
==========================================
+ Hits        16687    16713      +26     
- Misses       1486     1495       +9     

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[pitdicker]

Published 🎉.