Binary sensor for HA `annouce` flag in media_player

**Describe the problem you have/What new integration you would like**
Media player calls from HA can come with a binary parameter `annouce` set to `true`. We need to see this in ESPHome.

**Please describe your use case for this integration and alternatives you've tried:**
When the call arrives with `annouce` set to `true`, would be nice to have a binary sensor which can trigger some ESPHome automations, specific to the announcement. Like turn on a GPIO output to swicth on a different set of speakers, or increase volume, etc.

The binary sensor should be kept in ON state as long as the stream is playing, and should turn OFF together with the end of the stream.

**Additional context**

No files, tests, or entry points are identified in the request. Start by locating the ESPHome media_player handling for Home Assistant calls and its stream lifecycle, then determine how the annouce flag can drive a binary sensor. Done means the sensor stays on for the announcement stream, turns off when it ends, and can trigger automations.

Written by the indexing model from the issue text.