Add buffer integration test

Rearrange channel crate structure
Get channel buffer from database

co-authored-by: Max <max@zed.dev>

crates/collab_ui/src/collab_panel/channel_modal.rs

@@ -1,4 +1,5 @@
-use client::{proto, ChannelId, ChannelMembership, ChannelStore, User, UserId, UserStore};
+use channel::{ChannelId, ChannelMembership, ChannelStore};
+use client::{proto, User, UserId, UserStore};
 use context_menu::{ContextMenu, ContextMenuItem};
 use fuzzy::{match_strings, StringMatchCandidate};
 use gpui::{