fix(mistral): supports the default llms.WithTools implementation

[douglarek]

PR Checklist

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• Name your Pull Request title clearly, concisely, and prefixed with the name of the primarily affected package you changed according to Good commit messages (such as memory: add interfaces for X, Y or util: add whizzbang helpers).
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[douglarek]

cc @tmc

[tmc]

LGTM. Really need more robust coverage on this.