Add buffer integration test

Rearrange channel crate structure
Get channel buffer from database

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

crates/collab/src/tests.rs

@@ -1,14 +1,14 @@
 use crate::{
-    db::{test_db::TestDb, NewUserParams, UserId},
+    db::{tests::TestDb, NewUserParams, UserId},
     executor::Executor,
     rpc::{Server, CLEANUP_TIMEOUT},
     AppState,
 };
 use anyhow::anyhow;
 use call::{ActiveCall, Room};
+use channel::ChannelStore;
 use client::{
-    self, proto::PeerId, ChannelStore, Client, Connection, Credentials, EstablishConnectionError,
-    UserStore,
+    self, proto::PeerId, Client, Connection, Credentials, EstablishConnectionError, UserStore,
 };
 use collections::{HashMap, HashSet};
 use fs::FakeFs;
@@ -31,6 +31,7 @@ use std::{
 use util::http::FakeHttpClient;
 use workspace::Workspace;
 
+mod channel_buffer_tests;
 mod channel_tests;
 mod integration_tests;
 mod randomized_integration_tests;