Support streaming TTS for Assist in the app

[zolakt]

Is your feature request related to a problem? Please describe.

Not sure if this should be a bug report or a feature request, but either way, streaming TTS (from a LLM voice pipeline) doesn't work in the companion app. It waits for the whole text response to be generated, before it starts TTS.

However it does work if you open HA in a browser, not through the app.

Describe the solution you'd like

Companion app should support streaming TTS.

Describe alternatives you've considered, if any

In Android the only alternative is not to use the app at all, and use HA in the browser, which is cumbersome.

Additional context

[TimoPtr]

We need to implement it following the documentation of the events https://developers.home-assistant.io/docs/voice/pipelines/#events

StartEvent now contains the URL that we need to play and core will stream the data when available.

[alipsky]

Bumping this, this is the major source of latency on my android voice assistant. I can get local LLM to respond instantaneously, and TTS to stream on desktop browsers, but on android for LLM responses, voice assistant is basically unusable because streaming isnt supported! This would make voice assistants usable on many devices