Intensive CPU usage when opening a chat window with many voicemails

### Steps to reproduce

Opening a chat window with many ( 5-10) voicemails in it.

### Outcome

The CPU goes banana. If not many voicemails, it might actually freeze the app and the only way to fix is to kill the process and relaunch. For some reason i think this might be linked to the "sound wave profile" generation/preview of the audio message. Not sure, just a gut feeling about this.

### Operating system

Linux Mint 21.2 cinamon

### Application version

Element version: 1.12.20 Crypto version: Rust SDK 0.16.0 (65b585f), Vodozemac 0.9.0

### How did you install the app?

_No response_

### Homeserver

using my own homeserver

### Will you send logs?

No

Reproduce the issue by opening a chat containing 5–10 voicemails on Linux Mint 21.2, then inspect the voicemail sound wave profile generation and audio preview path while monitoring CPU use. Done means the chat opens without freezing or excessive CPU usage when several voicemails are present, with the behavior checked against the reported Element version.

Written by the indexing model from the issue text.