🚜 Update Pydantic models and try to DRY them out

[jefftriplett]

What started as a quick fix for us using Pydantic to help us validate our frontmatter files has grown a bit unwieldy.

In our bin/*.py folder we have a bunch of scripts that help us organize and run our conference. Several include copies of the same BaseModel but we never got around to trying to refactor these to work off of the same models.

A quick win would be to refactor some of these files to reference the same set of BaseModels.

[tim-schilling]

I'd recommend using the process.py models. When I was implementing the integrations for the online platform, those seemed to be the most complete and what I re-used.