feat: Implement LocalDate, OffsetDate and DateInterval

[chrisimcevoy]

I started out with the aim of porting missing tests and functionality for LocalDate, one thing led to another and...

I ended up fleshing out DateInterval and adding OffsetDate as well.

Noda Time provides LocalDate conversion methods to/from the BCL DateTime. Over in #160, I discussed how these might look in python.

Having thought about it some more, I don't think it makes sense to port those. The reason they exist in Noda Time has a lot to do with .NET not having a discrete date-only type until fairly recently. The existing conversions to/from datetime.date make more sense, and mirror the newer conversion methods to/from DateOnly in Noda Time. It's easier to add these later than it would be to remove them.

I believe this is the first time I've encountered a Noda Time type (DateInterval) which implements both Deconstruct and GetEnumerator, but I could be wrong. At any rate, I came to the conclusion in #248 that __iter__() in Pyoda Time should be reserved for GetEnumerator ports. It's probably more valuable than a deconstructor, which from one point of view is syntactic sugar for assignment which is easily achieved in Python in a more explicit way. Just need to revisit previously-ported classes at some point and make sure the project is consistent about that.

Related to:

• Conversions to stdlib types #160
• Porting Deconstruct/GetEnumerator to Python #248

[codecov]

Codecov Report

Attention: Patch coverage is 99.86376% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.46%. Comparing base (40d6fe1) to head (57ee9fc).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pyoda_time/_local_date_time.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #252      +/-   ##
==========================================
+ Coverage   96.27%   96.46%   +0.18%     
==========================================
  Files         260      263       +3     
  Lines       20149    20873     +724     
==========================================
+ Hits        19399    20135     +736     
+ Misses        750      738      -12     

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