It is not clear which voice messages I have listened to or not

### Steps to reproduce

1. In a room with voice messages, listen to some voice messages, but leave others for later
2. Navigate away from the room, then come back
3. Look for voice messages that you've listened to

### Outcome

#### What did you expect?
For it to be clear which voice messages I've heard before and which not

#### What happened instead?
All voice messages look like I haven't listened to them

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

develop.element.io

### Application version

_No response_

### Homeserver

_No response_

### Will you send logs?

No

Reproduce the issue on develop.element.io using the listed steps, then trace how voice-message listened state is stored when leaving and re-entering a room. Identify the relevant webapp entry point and existing tests, and consider the work complete when previously heard and unheard voice messages remain visually distinguishable after navigation.

Written by the indexing model from the issue text.