feat: smooth text streaming

[ammario]

Right now we display tokens as we get them, exposing the user to provider jitter.

My concept for fixing this is some kind of "smoothingBuffer" designed to always store
the last 250ms of tokens. There is an automatically adjusting dispersal rate that regulates the buffer to desired lookback.

[ibetitsmike]

We can add an intentional buffer to improve the fluidity of UX when streaming and maintain a stable rate of token rendering.