feat: llm tags for reasoning

[TobiasGleiter]

Summary

Add a ReActStep struct with llm tags and a typed ReActParser to the
agents/react package.

Changes

• Add ReActStep struct with llm tags for reasoning, action, input and final answer
• Add ReActParser as a typed instantiation of jsonout.NewParser[ReActStep]

Struct

type ReActStep struct {
Reasoning string json:"reasoning" llm:"reasoning,think"
Action string json:"action" llm:"action,required"
Input string json:"input" llm:"action_input,required"
Answer string json:"answer" llm:"final_answer,optional"
}

Depends On

• jsonout must support the llm tag with think, required, and optional options