fix: move indexed_field check earlier for image dataset

[zanussbaum]

we ignore indexed_field for image datasets but if passed and not overwritten before, we'd accidentally ignore the colorable field. This fixes NOM-1782

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:rocket:	This description was created by Ellipsis for commit d8b8c0124bcf65da6036ee9bdee22c48ebe0276c

Summary:

Moved indexed_field check earlier in AtlasDataset.create_index to ensure correct handling for image datasets and updated version in setup.py.

Key points:

• Moved indexed_field check earlier in nomic/dataset.py::AtlasDataset::create_index.
• Ensures indexed_field is set to _blob_hash before other operations for image datasets.
• Prevents accidental ignoring of the colorable field.
• Added a warning log if indexed_field is ignored for image datasets.
• Updated version in setup.py from 3.0.42 to 3.0.43.

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