Fix imports for model initialization and allow subsetting of clustering data types

[ehuan2]

Here is a total list of changes:

1. Add gitignore for Python files.
2. Remove circular dependency by moving import of from sccello.src.model_prototype_contrastive import PrototypeContrastiveForMaskedLM to load_model_inference.
3. Add a function to run the model loading as a test.
4. get_fracdata_sample to get a subset of the data instead.