fix: Improve unread separator animation

[SystemKeeper]

The idea here is basically:

• When we write a message from the device ourselves, we can already remove the unread separator when adding the temporary message, effectively doing it in the same animation
• When we have a unread separator and we receive message from ourselves (e.g. written from a different device), we now do it in the same update batch and not in a separate one

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI