Add regressions for fusion

[lintool]

Follow up to #2590

We've got something like:

python src/main/python/run_regression.py --index --verify --search --regression beir-v1.0.0-robust04.bge-base-en-v1.5.flat.onnx

Let's set up similar regression for fusion, using the classes just implemented in #2590

• option (a) - we use the same script src/main/python/run_regression.py and just jam the fusion feature in there?
• option (b) - we create a different script, like run_fusion.py for this?

I'm agnostic, but (b) seems more plausible?

Maybe something like:

src/main/python/run_fusion_regression.py --regression beir-fusion-config-file.yaml

And maybe the script already assumes you've already got the base run files in runs/... something like that?