feat: add support for LMDB molecular/materials science datasets from FAIR Chemistry

[amorehead]

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ℹ️ PR Description

What changes were made and why?

This pull request adds support for LMDB molecular/materials science datasets from FAIR Chemistry. This will enable users to load, analyze, and train models with datasets such as OMol25, OMat24, and OPoly26. The code changes made in this pull request should be fairly modular and unlikely to negatively impact other regions of the codebase.

How were the changes tested?

Dedicated molecular and materials science data loading unit tests were introduced at tests/ml/datasets/test_lmdb_dataset.py. All tests pass with the command pytest tests/ml/datasets. Credit goes to @Alex-Abrudan for testing that this branch enables model training with OMol25 using foundry.

Additional Notes

Thank you for preparing such a modular codebase! That made this implementation fairly straightforward.