Improve ScoringFile read methods

[nebfield]

Currently the only method of reading rows from a ScoringFile is by iterating over a generator of ScoreVariants by using the variants property.

This isn't particularly helpful for some applications, like validating scoring files, because the generator stops when the first exception in a scoring file is raised.

• Add a context managed read() method which returns a csv.DictReader ready for iteration (ino data validation done)
• Add a read_variants() method which calls read() and yields ScoreVariants from the dictionaries (data is validated)
• The variants property now just returns the generator from read_variants()
• Clean up simplfified read functions

[codecov]

Codecov Report

Attention: Patch coverage is 96.29630% with 1 line in your changes missing coverage. Please review.

Project coverage is 89.66%. Comparing base (f570666) to head (f23e044).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...catalog.core/src/pgscatalog/core/lib/scorefiles.py	96.29%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #59      +/-   ##
==========================================
+ Coverage   89.61%   89.66%   +0.04%     
==========================================
  Files          54       53       -1     
  Lines        3467     3425      -42     
==========================================
- Hits         3107     3071      -36     
+ Misses        360      354       -6     

Flag	Coverage Δ
pgscatalog.core	92.78% <96.29%> (+0.18%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.