fix: manage silence for new SSRC with existing user_id

[rclaveau-tech]

Summary

Hi Team, thanks for your amazing work, I hope this PR will find you well.

When some events occurred like leaving a voice channel or having a network interrupt, when the user join again there is a new SSRC, so the code treat that like a new user joining, so the silence is not correctly sync.
This PR aiming to change the dict key to user_id and provide the correct silence between previous and new SSRC.

Information

• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed).
• This PR is not a code change (e.g. documentation, README, typehinting,
  examples, ...).

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
• I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.
• I have updated the changelog to include these changes.