Support for Surrogate Modeling Toolbox Machine Learning (GENN) Models

[bpaul4]

Fixes/Addresses:

Summary/Motivation:

Changes proposed in this PR:

• Demonstrates how users can train/save Surrogate Modeling Toolbox gradient-enhanced neural network (GENN) models with custom objects and produce .pkl files compatible with the ML AI Plugin in FOQUS
• Support for Surrogate Modeling Toolbox GENN models in FOQUS, including updates to the run methods, node properties, test framework, documentation and optional dependencies list

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[bpaul4]

There is one expected error. The "Build docs" check will fail until #1164 is merged, as the documentation in this PR includes a reference to a page that is added in the Gradient Generation PR. The "ReadTheDocs" check will fail for the same reason. The reference that doesn't exist yet is called gengrad.

[codecov]

Codecov Report

Attention: 22 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
foqus_lib/conftest.py	90.52% <ø> (ø)
foqus_lib/framework/ml_ai_models/mlaiSearch.py	82.92% <ø> (ø)
foqus_lib/framework/graph/node.py	62.37% <65.62%> (-0.25%)	⬇️

... and 15 files with indirect coverage changes

📢 Thoughts on this report? Let us know!.

[lbianchi-lbl]

• I left one minor suggestion which is fully optional
• The rest of the code and docs looks fine as far as I could tell from a quick skim

[lbianchi-lbl]

I've just checked, and the minor drop in code coverage seems to be coming from error handling code being added (and I'm not sure whether this is also due to part of the report still missing), so I'm merging this in.