Upgrade to pydantic v2

[demeringo]

Problem

Actual codebase is dependent on pydantic v1 which is now deprecated in favor of pydantic v2.

This block the upgrade of fastapi #313

Solution

Update to pydantic v2. Not sure if we need it but a tool exists to migrate the codebase.

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

Alternatives

Additional context or elements

[demeringo]

I attempted to migrate the code using the bump-pydantictool provided.

https://github.com/pydantic/bump-pydantic

It seems to work fine.

[demeringo]

Closed by #315