Convert NaiveDate::from_num_days_from_ce to return Result

[Zomtir]

This pull request targets the issue #1469. The implementation is based on the discussion in #1445.

• Convert NaiveDate::from_num_days_from_ce to return Result
• i32::checked_add() is mapped locally to an Err(Error::OutOfRange) for now

cc @pitdicker

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.34%. Comparing base (999582e) to head (bd44d85).

Additional details and impacted files

@@            Coverage Diff             @@
##            0.5.x    #1470      +/-   ##
==========================================
- Coverage   94.34%   94.34%   -0.01%     
==========================================
  Files          37       37              
  Lines       17009    17007       -2     
==========================================
- Hits        16047    16045       -2     
  Misses        962      962              

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[pitdicker]

It may be for the best that you didn't start with the timestamp methods on NaiveDateTime #1471.

[pitdicker]

Your first one in 🎉.