Forbid inheritance from SourceProxy

[knoepfel]

The SourceProxy class is not intended for inheritance. In our migration away from SourceProxy, forbidding inheritance from it will cleanup the workflows.

N.B. This PR cannot be merged in until issue https://github.com/HEPCloud/decisionengine_modules/issues/363 is resolved. It will be in draft state until then.

[codecov[bot]]

Codecov Report

Merging #526 (024f744) into master (e95071f) will increase coverage by 0.29%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #526      +/-   ##
==========================================
+ Coverage   83.83%   84.12%   +0.29%     
==========================================
  Files          48       48              
  Lines        3099     3100       +1     
  Branches      483      482       -1     
==========================================
+ Hits         2598     2608      +10     
+ Misses        463      460       -3     
+ Partials       38       32       -6     

Flag	Coverage Δ
python-3.10	83.58% <100.00%> (+0.13%)	:arrow_up:
python-3.6	83.36% <100.00%> (+0.19%)	:arrow_up:
python-pypy-3.7	83.59% <100.00%> (+0.23%)	:arrow_up:

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

Impacted Files	Coverage Δ
...rc/decisionengine/framework/modules/SourceProxy.py	71.01% <100.00%> (+6.30%)	:arrow_up:
.../decisionengine/framework/engine/DecisionEngine.py	90.48% <0.00%> (+0.48%)	:arrow_up:
src/decisionengine/framework/dataspace/maintain.py	100.00% <0.00%> (+0.95%)	:arrow_up:
src/decisionengine/framework/engine/Workers.py	90.27% <0.00%> (+2.77%)	:arrow_up:

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[mambelli]

I'd set this as draft until the blocking issue is fixed. I think only the opener can change that

[knoepfel]

Placed in draft state until https://github.com/HEPCloud/decisionengine_modules/issues/363 is resolved.