feat(inference): add Mistral remote inference provider

[NishchayMahor]

What does this PR do?

Adds a remote inference provider for Mistral AI (remote::mistral). Mistral is a major frontier lab that wasn't yet in the inference lineup — this lets users run Mistral chat models (e.g. mistral-large-latest, mistral-small-latest, codestral-latest) and the mistral-embed embedding model through the standard inference API.

Mistral exposes an OpenAI-compatible chat-completions and embeddings API, so the adapter extends the shared OpenAIMixin pointed at https://api.mistral.ai/v1, authenticated via MISTRAL_API_KEY (or the mistral_api_key provider-data header). No new pip dependency is required.

Changes

• providers/remote/inference/mistral/ — adapter (MistralInferenceAdapter), config (MistralImplConfig + provider-data validator), and get_adapter_impl.
• Registered remote::mistral in providers/registry/inference.py.
• Unit tests in tests/unit/providers/inference/test_mistral_config.py.
• Regenerated provider docs (docs/.../inference/remote_mistral.mdx) via scripts/provider_codegen.py.

Test Plan

• pytest tests/unit/providers/inference/test_mistral_config.py → 5 passed (default/custom/env base URL, sample run config, provider-data + embedding metadata).
• Provider resolves from the registry (remote::mistral) and imports cleanly.
• mypy and ruff clean on the new module; docs codegen produces the expected page.

Usage:

providers:
  inference:
  - provider_id: mistral
    provider_type: remote::mistral
    config:
      api_key: ${env.MISTRAL_API_KEY}