Bump pydantic to 2.5.2

What does this merge request do and why?

This MR bumps pydantic from 1.10.13 to 2.5.2. This upgrade also ensure compatibility with FastAPI moving forward. Pydantic V2 support has been added since FastAPI 0.100.0. Pydantic V1 will be deprecated in the future.

This update also requires to bump Langchain related dependencies to be compatible with Pydantic v2. Code mods are mostly generated using bump-pydantic library.

• Full pydantic changeset
• Full langchain changeset
• Full langserve changeset

More details for the migration is at https://docs.pydantic.dev/latest/migration/.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.

Closes #355 (closed)