Make UnlikelyLogger as interface instead of struct

[xalanq]

https://github.com/livekit/protocol/blob/c0c2e6e03dcc9e8b5d75568b78b91f73d8fd0d6e/logger/logger.go#L103C1-L103C29

Interface Logger has an method WithUnlikelyValues which returns a UnlikelyLogger with two private fields logger and keysAndValues. But the UnlikelyLogger is not an interface, there is no way to mock or reimplement the Logger because of this.