Add range checks to Parsed::set and hide fields in docs

[pitdicker]

This does not remove the range checks from the Parsed::to_* methods, because as long as the fields are public they can be set to an out of range value. Something to do on the 0.5.x branch.

[codecov]

Codecov Report

Attention: Patch coverage is 70.46632% with 57 lines in your changes are missing coverage. Please review.

Project coverage is 91.93%. Comparing base (e292d9b) to head (23a65df).
Report is 15 commits behind head on main.

❗ Current head 23a65df differs from pull request most recent head 15f7e62. Consider uploading reports for the commit 15f7e62 to get more accurate results

Files	Patch %	Lines
src/format/parsed.rs	70.46%	57 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1465      +/-   ##
==========================================
- Coverage   92.16%   91.93%   -0.24%     
==========================================
  Files          40       40              
  Lines       18052    18218     +166     
==========================================
+ Hits        16637    16748     +111     
- Misses       1415     1470      +55     

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[pitdicker]

@djc When you have time, can you look at the direction of the documentation in the last commit? Then I'll merge squash it into the right commit.

I would like to start building on top of this PR 😄.

[djc]

Let's add these below the to_* methods, since they're pretty trivial?