Add collapse_reasoning to natively fold reasoning while streaming

[joaomendoncaa]

it would be incredibly awesome to have a collapse_reasoning (inspired by #1614)

inspired by all other chat UIs right now; natively folding the reasoning header and the contents below, only showing a couple of the latest streamed lines at any point in time while it's streaming reasoning, and keeping it folded when reasoning eventually finishes

1. responses can be long and annoying to skim through, even worse when you have a huge wall of reasoning
2. with this solution, we wouldn't hide reasoning, but natively fold it, giving users the option to unfold it as they desire when they desire

would this be something of interest @olimorris?

[olimorris]

This would be very interesting. But I'd want to combine it with folding the context panel as well. The latter would benefit the majority of users.

[olimorris]

As an aside, I'm going to look into adding this for tool output in the next week.

[joaomendoncaa]

any news on this? if the scope is well defined you can shoot it towards me, and I might take a stab at it