Add base_url to Mistral Provider

[alibeyram]

passing base_url to support mistral models that are hosted somewhere else (e.g. Azure)

I tested this and it works

from pydantic_ai import Agent
from pydantic_ai.models.mistral import MistralModel
from pydantic_ai.providers.mistral import MistralProvider

model = MistralModel(
    "mistral-small-2503",
    provider=MistralProvider(
        api_key=os.environ["AZURE_AI_API_KEY"], base_url=os.environ["AZURE_AI_ENDPOINT"]
    ),
)

agent = Agent(model)

[DouweM]

@alibeyram Thank you! Can you please address the failing CI check by documenting the new attribute in the docstring? And for consistency with OpenAIModel, update the error logic about passing base_url not being mutually compatible with passing http_client? Finally, this deserves some documentation in the Mistral provider docs, similar to what we have for OpenAI.

[hyperlint-ai]

PR Change Summary

Added support for specifying a base URL in the Mistral Provider to accommodate models hosted on external platforms like Azure.

• Introduced base_url parameter in MistralProvider for external model support
• Updated example code to demonstrate usage of base_url with Azure
• Modified documentation to reflect changes in MistralProvider

Modified Files

• docs/models/mistral.md

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[alibeyram]

@DouweM ok I did all of them.

[DouweM]

@alibeyram Thanks Ali!