provide Python support for new product api

[wlav]

This re-enables Python after adding support for the new product query API (#267). Note that there are a few more things added into the mix, that fit here:

• Added support for different layers (prior, the layer was hard-wired and everything happened in either "job" or "event"). This goes along because the new product query makes the layer explicit, allowing for straightforward specification in the configuration.
• Added support for JSON objects in the configuration wrapping. This to support the above.
• Removal of code duplication introduced by Improve test coverage for Python support #213. This fits here because the duplicated code would otherwise need to be updated to the new product query API, so its removal shrinks the amount of refactoring needed.
• Updates for test coverage; somewhat unrelated but the removal of duplicated code that was tested drops the overall ratio. This corrects some of that.

[wlav]

@phlexbot format

[github-actions]

No automatic jsonnetfmt fixes were necessary.

[github-actions]

No automatic markdownlint fixes were necessary.

[github-actions]

No automatic cmake-format fixes were necessary.

[github-actions]

No automatic clang-format fixes were necessary.

[greenc-FNAL]

Review the full CodeQL report for details.

[codecov]

Codecov Report

❌ Patch coverage is 72.72727% with 69 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
plugins/python/src/modulewrap.cpp	71.04%	38 Missing and 26 partials ⚠️
plugins/python/src/configwrap.cpp	83.33%	3 Missing and 2 partials ⚠️

❌ Your patch status has failed because the patch coverage (72.72%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

@@            Coverage Diff             @@
##             main     #369      +/-   ##
==========================================
- Coverage   86.51%   83.57%   -2.95%     
==========================================
  Files         119      126       +7     
  Lines        2403     3232     +829     
  Branches      387      579     +192     
==========================================
+ Hits         2079     2701     +622     
- Misses        206      322     +116     
- Partials      118      209      +91     

Flag	Coverage Δ
unittests	83.57% <72.72%> (-2.95%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
plugins/python/src/errorwrap.cpp	79.54% <ø> (ø)
plugins/python/src/pymodule.cpp	60.81% <100.00%> (ø)
plugins/python/src/wrap.hpp	100.00% <ø> (ø)
plugins/python/src/configwrap.cpp	85.56% <83.33%> (ø)
plugins/python/src/modulewrap.cpp	71.30% <71.04%> (ø)

... and 10 files with indirect coverage changes

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