DM-33489: Implement unit tests for QuantumBackedButler

[andy-slac]

This also needed few changes to QBB classes to support serialization of
the provenance data.

Checklist

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

[codecov]

Codecov Report

Merging #672 (6d64208) into main (8026ae2) will increase coverage by 0.49%.
The diff coverage is 96.30%.

@@            Coverage Diff             @@
##             main     #672      +/-   ##
==========================================
+ Coverage   83.76%   84.26%   +0.49%     
==========================================
  Files         241      242       +1     
  Lines       30729    30968     +239     
  Branches     5156     5216      +60     
==========================================
+ Hits        25739    26094     +355     
+ Misses       3828     3707     -121     
- Partials     1162     1167       +5     

Impacted Files	Coverage Δ
...ython/lsst/daf/butler/registry/bridge/ephemeral.py	88.88% <66.66%> (ø)
...thon/lsst/daf/butler/registry/bridge/monolithic.py	84.53% <66.66%> (ø)
python/lsst/daf/butler/core/storedFileInfo.py	85.29% <87.50%> (-1.07%)	⬇️
python/lsst/daf/butler/_quantum_backed.py	89.88% <94.73%> (+89.88%)	⬆️
tests/test_quantumBackedButler.py	98.45% <98.45%> (ø)
python/lsst/daf/butler/__init__.py	100.00% <100.00%> (ø)
python/lsst/daf/butler/datastores/fileDatastore.py	80.63% <100.00%> (+0.56%)	⬆️
tests/test_quantum.py	97.40% <100.00%> (ø)
python/lsst/daf/butler/core/datastore.py	74.52% <0.00%> (+0.47%)	⬆️
... and 3 more

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[TallJimbo]

Looks good! Only minor comments, though if we do have an import cycle I don't want to wait too long to get it fixed.