Support langchain v1.0

[sentrivana]

langchain is currently in 0.x, but there are prereleases available for 1.0. Our integration doesn't work out of the box with the prereleases. Find out what has changed and adapt the integration.

Once this is done, if #4734 has been merged already, remove these two restrictions from scripts/populate_tox/config.py. You can also test the integration on 1.0 this way.

[linear]

PY-1821 Support langchain v1.0

[sentrivana]

Draft PR that runs CI against the current v1 alpha is here: #4874

I'll postpone working on this until v1 is out of alpha. As it stands the package is in a weird state, I can't trace some of the changed imports anywhere. There is also no migration guide yet. Will keep an eye out for the first beta/RC.

Releases: https://pypi.org/project/langchain/#history
Migration guides (on what seems to be the 1.0 branch): https://github.com/langchain-ai/langchain/blob/wip-v1.0/MIGRATE.md