idea: Render CoT/reasoning for remote/custom providers

[david-menloai]

Problem Statement

with remote models which support CoT, Jan receives the data, just don't render it Can we support this feature?

Feature Idea

with remote models which support CoT, Jan receives the data, just don't render it Can we support this feature?

[qnixsynapse]

For nonstreaming data, The reasoning is in choices[0].message.reasoning_content in deepseek format.

For streaming data, it's in choices[0].delta.reasoning_content.

This structure depends on model's chat template. Not all reasoning models do this but this is getting the norm.

[LazyYuuki]

Will be addressed by #5775