Create Schema / Pydantic Models for Theory Data

TODOs:

• Take the current theory data repo and use the processed data files (example here)

• Create schemas around the 4 files using Pydantic

  • mean_field.json
  • imsrg_solution.json
  • results.json
  • metadata.csv

• Store as module in the repo (src/pd4m-api/schemas/ directory)