sciarg: fix partitioning

[ArneBinder]

This PR

• adds a test that asserts label counts for labeled_partitions
• changes RegexPartitioner pattern to "<([^>/]+)>(?s:.)*?</\\1>": find matching tags non-greedy (*?), allow newlines in between (s flag) and capture the tag name

This affects only document A32 where the abstract was not identified before but now it is.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (06e3af5) to head (3086c6a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #159      +/-   ##
===========================================
+ Coverage   92.46%   100.00%   +7.53%     
===========================================
  Files          10         1       -9     
  Lines         916        49     -867     
===========================================
- Hits          847        49     -798     
+ Misses         69         0      -69     

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