common : add parser for ministral/mistral large 3

[aldehir]

Note

This is intended to be an functional demonstration of the PEG parser implemented in #17136, and as such depends on that PR. I have squashed the commits down to make it easy to view the parser implementation for Ministral 3 Reasoning/Instruct and Mistral Large 3 Instruct.

Parser implementation for Ministral 3 Reasoning/Instruct and Mistral Large 3 Instruct. It deviates from the previous Mistral outputs by generating tool calls in the form: [TOOL_CALLS]tool_name[ARGS]{"arg1": ... }...

Features

• Extracts reasoning to reasoning_content¹
• Formats system and assistant messages containing reasoning_content into {"type": "thinking", "thinking": "..."} content blocks the chat template expects. server: thinking type rejected as invalid but used by Ministral 3 #17700
• Supports tool calling for both tool_choice = auto and tool_choice = required (with thinking).
• Supports parallel tool calls
• Supports response_format with thinking.

Keeping this as a draft until #17136 gets the stamp of approval.

Footnotes

1. Currently only reasoning_format = auto/deepseek is supported. I was unaware the reasoning format is not exposed during chat param init, but this is easy to address. ↩