Pydantic v1 and v2 support

[eyurtsev]

Make kor pydantic v1 and v2 compatible.

Additional changes:

• No more validation on node ids -- makes it easier to use node ids in other languages (e.g., chinese)
• Add testing to CI to test with both v1 and v2

Not fully implemented:

• Support for serialization via parse_obj

[eyurtsev]

https://github.com/eyurtsev/kor/issues/206