[WIP] Updating the API client

[esoteric-ephemera]

Completed:

• Reorganize client into modules for easier editing
• Replace some quasi-deprecated packages in favor of those already in the stack:
  • ujson in favor of orjson (req'd by pymatgen)
• Align the syntaxes of the main API client and the MPC client (i.e., consistent naming of class kwargs)

Planned:

• Updating client structure + lessening dependency stack to be more future proof
• Pydantic models for returned data types? Possibly just pandas