feat(ChatMistralAI): add parallel tool calling, verbose API, add missing converter for tool call result content

[xu-chris]

This PR solves three things when using Mistral:

1. Tool call results might be a list. The current implementation wasn't able to handle that
2. While doing so, I have realized that Mistral calls tools in parallel. Mistral supports parallel_tool_calls - like OpenAI does
3. verbose_api was a required addition for easier bug fixing

I did use Claude Opus 4.5 for creating the changes. I tried to align them as close as possible to the ChatOpenAI module.

Hope this PR meets your quality standard. 🙏

[xu-chris]

I've realized that this PR might duplicate solutions of @arjan / PR #417 .
@brainlid Do you need a hand to check and merge the PRs?

[arjan]

Yep I created #416, #417 and #418 for these, they overlap indeed..

[xu-chris]

Closed because of overlapping PRs.
Edit: Opened #433 for handling parallel tool calls