Pydantic V2

[zyr17]

Upgrade to Pydantic V2 by following steps.

• [ ] install pydantic 2.x, and include from pydantic.v1, so pydantic can be always up-to-date, and no need to maintain two environments when upgrading to v2.
• [ ] wait until a better way to supprt duck-typing serialization of pydantic v2 is proposed by official. Otherwise too many inherit classes are subject to change, and current tests cannot find bugs on this problem.
• [ ] performance evaluation between v1 and v2. Initial comparism results show that v2 spends about 2x time in initializing, but have extreamly high performance on output json data. Not sure the performance difference during simulation.

[zyr17]

Pydantic 2.7 will introduce "serialize_as_any" method, check whether it can work.