Depreciated Import

[featurlizer.py](https://github.com/AI-multimodal/OmniXAS/blob/dcdb50132eefa2ba704e4a23d55ec73b8b919032/omnixas/featurizer/m3gnet_featurizer.py#L54)

` omnixas.utils.constants` is depreciated. 

Fix: 
```python
from omnixas.core.periodic_table import Element, SpectrumType
```

