Add buffer integration test

Rearrange channel crate structure
Get channel buffer from database

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

crates/collab_ui/Cargo.toml

@@ -26,6 +26,7 @@ auto_update = { path = "../auto_update" }
 db = { path = "../db" }
 call = { path = "../call" }
 client = { path = "../client" }
+channel = { path = "../channel" }
 clock = { path = "../clock" }
 collections = { path = "../collections" }
 context_menu = { path = "../context_menu" }

crates/collab_ui/src/collab_panel.rs

@@ -4,10 +4,8 @@ mod panel_settings;
 
 use anyhow::Result;
 use call::ActiveCall;
-use client::{
-    proto::PeerId, Channel, ChannelEvent, ChannelId, ChannelStore, Client, Contact, User, UserStore,
-};
-
+use channel::{Channel, ChannelEvent, ChannelId, ChannelStore};
+use client::{proto::PeerId, Client, Contact, User, UserStore};
 use context_menu::{ContextMenu, ContextMenuItem};
 use db::kvp::KEY_VALUE_STORE;
 use editor::{Cancel, Editor};

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::{