Compatibility with LangChain 0.2.0

I would like to use ragatouille with langchain 0.2.0 (released 3 days ago).

When I try to install ragatouille using poetry in an environment already containing langchain 0.2.0, I get this:
```
Because ragatouille (0.0.8.post2) depends on langchain (>=0.1.0,<0.2.0)
and no versions of ragatouille match >0.0.8.post2,<0.0.9, ragatouille (>=0.0.8.post2,<0.0.9) requires langchain (>=0.1.0,<0.2.0).
```

Right now, in ragatouille's [pyproject.toml](https://github.com/bclavie/RAGatouille/blob/main/pyproject.toml) there are these version specifications:
```
langchain_core = "^0.1.4"
langchain = "^0.1.0"
```

I don't know if the langchain update will require serious changes or it will be straigthforward, but I'm looking forward to it!

Thanks for your attention!

Start with pyproject.toml and reproduce the Poetry dependency conflict in an environment containing langchain 0.2.0. Inspect the declared langchain and langchain_core constraints, then verify that the package installs successfully with the requested version and that existing compatibility checks, if present, still pass.

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