OPSIM-1184: use ra/dec to order series of observations in BlobSurvey

[yoachim]

Eliminate an unnecessary ra,dec to alt,az conversion. Was probably originally stuck in there at some point because of a degrees,radians issue downstream.

[ehneilsen]

Looks fine, as far as I can tell. A test to verify that the change doesn't change the resultant order for some sample sets of observations would be reassuring.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.09%. Comparing base (71cbc4a) to head (30ce4e6).
Report is 58 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #95      +/-   ##
==========================================
- Coverage   72.89%   72.09%   -0.81%     
==========================================
  Files         137      143       +6     
  Lines       13583    14891    +1308     
  Branches     1870     2061     +191     
==========================================
+ Hits         9902    10736     +834     
- Misses       3269     3722     +453     
- Partials      412      433      +21     

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