Add support for Pydantic 2

[MatthewScholefield]

This adds support for Pydantic 2 in a backwards compatible way.

For anyone who wants to use this before it is merged, you can do:

pip3 install --upgrade git+https://github.com/MatthewScholefield/pydantic-sqlalchemy.git@master#egg=pydantic-sqlalchemy

I know there's a PR to add a notice to the README to deprecate the project, but I still feel the project is useful for cases where SQLModel isn't yet complete (ie. migrations which the docs are currently yet-to-be-written).

[Jypear]

I'm dealing with a PR that just so happens to use this package and noticed this PR exists. Just out of interest is there plans for this PR to be merged still? As the changes resolve a couple of depreceation warnings I'm getting. If not I'll probably just fork this as it seems to only be a small use case.

[tiangolo]

Thanks for the interest! And thanks for the patience with my reply. :sweat_smile:

I deprecated this library a while ago in favor of SQLModel which would solve all the same use cases in a much better way, and I'm directing all the effort in that direction, so sadly I wouldn't be able to take new features here (that would also need maintaining them).

Given that, I'll close this one, but thanks for the effort! :coffee:

Also, thanks for adding instructions for people to install your branch and test it, it might be useful for them during migrations.