Fix exposure time accounting

[gbrammer]

The EXPTIME keyword of the spectra combined and extracted with slit_combine double counted the exposure times for cases with contributions from both NRS1 and NRS2 detectors. This update fixes the accounting.

Also includes updates to msaexp.cloud for passing additional keyword parameters stored in the database.

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 8 lines in your changes missing coverage. Please review.

Project coverage is 51.43%. Comparing base (92b1aa6) to head (6ef71c2).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
msaexp/slit_combine.py	55.55%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #90      +/-   ##
==========================================
- Coverage   51.45%   51.43%   -0.03%     
==========================================
  Files          16       16              
  Lines        7851     7859       +8     
==========================================
+ Hits         4040     4042       +2     
- Misses       3811     3817       +6     

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