text: Title: Add providers classes for `mistralai`, `cohere`, `anthropic` and `groq`
  Body: At the moment, we have the models for all of them, but since we introduced the `Provider`s classes, we missed the ones for:
  
  - [x] MistralAI https://github.com/pydantic/pydantic-ai/pull/1118
  - [ ] Cohere
  - [x] Anthropic
  - [x] Groq: https://github.com/pydantic/pydantic-ai/pull/1084
  
  PR welcome.