Fix two more issues with ScopeSimple

[teutoburg]

The bang-keys in meta in SummedExposure were somehow overwritten with the corresponding cmds values in the ExtraFitsKeywords, this should no longer occur. The previously added 3rd level in cmds makes the hack in scopesimple obsolete.

The default instrument mode wasn't actually applied by scopesimple, because of a mistreatment of an empty iterator. Fixed that and added tests to verify.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.99%. Comparing base (4309816) to head (97305a7).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #514      +/-   ##
==========================================
- Coverage   77.06%   76.99%   -0.07%     
==========================================
  Files          66       66              
  Lines        8218     8213       -5     
==========================================
- Hits         6333     6324       -9     
- Misses       1885     1889       +4     

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[hugobuddel]

I didn't see the actual iterator. Maybe it would be better to fix it there by immediately using a list? Nevertheless, if this works for now, then fine with me.