Declare scikit-learn as an optional dependency

[nathanjmcdougall]

scikit-learn is used in the pyemu.emulators module, among other places:

pyemu/pyemu/emulators/__init__.py

Lines 47 to 55 in 5dd3c78

	raise ImportError("LPFA emulator requires scikit-learn. Install with: pip install scikit-learn")
	class GPR:
	def __init__(self, *args, **kwargs):
	raise ImportError("GPR emulator requires scikit-learn. Install with: pip install scikit-learn")
	class StandardScalerTransformer:
	def __init__(self, *args, **kwargs):
	raise ImportError("StandardScalerTransformer requires scikit-learn. Install with: pip install scikit-learn")

graphviz is just used in misc\graph_pyemu.py.

[coveralls]

coverage: 77.921% (+0.05%) from 77.871%
when pulling 50017c3 on nathanjmcdougall:fix/declare-scikit-learn-as-an-optional-dep
into 5dd3c78 on pypest:develop.

[briochh]

my feeling is that the graph_pyemu isn't picked up anywhere. Let's check in with @aymanalz, we maybe be able to utilise it or drop graphviz as a dependancy.

[nathanjmcdougall]

Yeah I get the impression that the module there is intended for as a dev tool - to visualize the architecture of the modules.

I think it would be helpful to adopt dependency-groups from PEP 735 to give dedicated declaration sections for dev dependencies that aren't relevant for consumers of pyEMU as a package, but only for developers of pyEMU itself. Similarly, the test dependencies would probably be better as in a dependency-groups group than as optional dependencies.

This would allow us to declare lint dependencies etc. (e.g. if Ruff gets added) and so graphviz could be declared without adding it to the actual dependencies of the package. I'd put in a separate PR for that if you want it.

[briochh]

I have a fork, that is slowly (and tentatively) exploring a move to uv for the whole project, and thus an updated (and more responsible pyproject.toml) https://github.com/briochh/pyemu/tree/feat_uv . perhaps we can bite the bullet on that at some point.

[nathanjmcdougall]

That would be excellent. Probably in that case, we can hold off on declaring graphviz for now. I'll revert it when I get a moment.

[aymanalz]

Thank you for checking about Graphviz dependency. I do not think I will use this package.