Improve get_subsets performance for single subset case

[rosteen]

As previously noted in the deleted comment, there's no need to process every subset if only one subset was requested. This trims the list down to only the matching subset before going through the loop processing them all.

[pllim]

Code looks like code. Thanks!

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.76%. Comparing base (629fa62) to head (9999179).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
jdaviz/app.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3363      +/-   ##
==========================================
- Coverage   88.77%   88.76%   -0.01%     
==========================================
  Files         125      125              
  Lines       19227    19231       +4     
==========================================
+ Hits        17068    17071       +3     
- Misses       2159     2160       +1     

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

[javerbukh]

Yup, definitely code. LGTM!