[Frontend] Responses api harmony output

[alecsolder]

Purpose

This PR is meant to optionally expose Harmony messages when using the Responses API. These messages are useful for debugging or understand what exactly a model is doing under the hood. There are concepts in Harmony that to not translate 1:1 with Responses API output (metadata like Harmony channel, or full messages like built in tool call output, etc)

Test Plan

Tested with Unit tests and gpt-oss model

Test Result

(Not done yet, still in draft)

[github-actions]

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @alecsolder.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork