DM-40242: skip existence checks for quantum inputs that have datastore records

[TallJimbo]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 3 lines in your changes missing coverage. Please review.

Project coverage is 90.03%. Comparing base (e4484fe) to head (7fe3f9d).
Report is 3 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
python/lsst/ctrl/mpexec/singleQuantumExecutor.py	81.25%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #318   +/-   ##
=======================================
  Coverage   90.03%   90.03%           
=======================================
  Files          50       50           
  Lines        4536     4567   +31     
  Branches      414      420    +6     
=======================================
+ Hits         4084     4112   +28     
- Misses        327      328    +1     
- Partials      125      127    +2     

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[andy-slac]

Looks good.