Update to pydantic v2

[danielballan]

Pydantic provides an automated migration tool that should do the bulk of the work in an automated way, such that we can:

1. Run the tool.
2. Run our test suite.
3. Fix whatever broke.

https://docs.pydantic.dev/latest/migration/

This is worth doing soon, as event-model recently updated to pydantic 2.0.

[danielballan]

There is a duplicate issue that I created when we first pinned pydantic back to <2: #491