[BUG] MistralAIModel throws import error due to deprecated class

[Jgilhuly]

Describe the bug Defining a MistralAIModel as an eval model throws an error. It looks like this is because mistalai.exceptions is no longer in the mistral package.

To Reproduce MRE:

from phoenix.evals import (
    MistralAIModel,
    RelevanceEvaluator,
)

relevance_evaluator = RelevanceEvaluator(MistralAIModel)

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