Move jsonargparse to main dependencies, lazy-load sklearn/scipy in PubChem

[Copilot]

Inference-only installations failed due to missing jsonargparse (required by Lightning CLI) and scikit-learn imports in PubChem dataset module being eagerly evaluated at import time.

Changes

Dependencies (pyproject.toml)

• Move jsonargparse[signatures]>=4.17 from [dev] to main dependencies

Lazy imports (chebai/preprocessing/datasets/pubchem.py)

• Move sklearn.cluster.KMeans import into PubChemKMeans._build_clusters() and cluster_centers_superclustered property
• Move sklearn.model_selection.train_test_split into PubChem.setup_processed() and PubChemTokens.setup_processed()
• Move scipy.spatial import into PubChemKMeans._exclude_clusters()

This allows importing PubChem classes without requiring sklearn/scipy to be installed, deferring the dependency until dataset methods that actually use these libraries are called.

# Now works without sklearn installed
from chebai.preprocessing.datasets.pubchem import PubChem

# sklearn only required when calling setup_processed() or other split/clustering methods

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add jsonargparse to main dependencies, only use sklearn if needed</issue_title>
<issue_description>We had two issues when installing chebai for inference only:

• missing jsonargparse caused some error in lightning
• missing scikit-learn causes issues with the pubchem dataset

Both dependencies are included in the [dev] extra.

Todo

• move jsonargparse to the regular dependencies
• only load sklearn when a PubChem dataset is actually instantiated</issue_description>

Comments on the Issue (you are @copilot in this section)

@aditya0by0 Lets try and assign this to co-pilot to check whether it can take upon minor issues.

• Fixes Add jsonargparse to main dependencies, only use sklearn if needed #151

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