Refactor internals module part 3

[pitdicker]

The first commit makes the iso_week_from_yof function a method on IsoWeek.
The next changes it to consume an ordinal and year_flags instead of Of, and inlines the functionality that was in Of::isoweekdate_raw.

The others move over the weekday and year_flags getters to NaiveDate.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (5ba8ed1) 91.84% compared to head (df2e6f7) 91.84%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/naive/date.rs	95.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1431   +/-   ##
=======================================
  Coverage   91.84%   91.84%           
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  Files          38       38           
  Lines       17628    17571   -57     
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- Hits        16190    16138   -52     
+ Misses       1438     1433    -5     

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