[CS 598]: Add CAMELOT Model

[meeramehta]

CAMELOT model integration: add model, tests, docs, and packaging updates

Summary

• Add a new CAMELOT model implementation (pyhealth.models.CAMELOTModule) for cluster-based feature importance on EHR time-series.
• Export the model from pyhealth.models and add API docs.

Changes

• New model file: pyhealth/models/camelot.py
• Unit tests: tests/core/test_camelot.py (initialization, forward passes, parameter checks, and cluster loss functions)
• Documentation: docs/api/models/pyhealth.models.CAMELOTModule.rst and added to docs/api/models.rst
• Packaging: add "lightning" to pyproject.toml and pixi feature dependencies
• Export: updated pyhealth/models/init.py to include CAMELOTModule

Notes

• Tests exercise basic functionality (inference/training forward, device, and cluster losses).
• Adds a dependency on the Lightning package; ensure CI environment includes it.