Add buffer integration test

Rearrange channel crate structure
Get channel buffer from database

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

crates/rpc/proto/zed.proto

@@ -142,6 +142,9 @@ message Envelope {
         GetChannelMembersResponse get_channel_members_response = 128;
         SetChannelMemberAdmin set_channel_member_admin = 129;
         RenameChannel rename_channel = 130;
+
+        GetChannelBuffer get_channel_buffer = 131;
+        GetChannelBufferResponse get_channel_buffer_response = 132;
     }
 }
 
@@ -948,6 +951,15 @@ message RenameChannel {
     string name = 2;
 }
 
+message GetChannelBuffer {
+    uint64 channel_id = 1;
+}
+
+message GetChannelBufferResponse {
+    string base_text = 1;
+    repeated Operation operations = 2;
+}
+
 message RespondToChannelInvite {
     uint64 channel_id = 1;
     bool accept = 2;

crates/rpc/src/proto.rs

@@ -248,7 +248,9 @@ messages!(
     (GetPrivateUserInfo, Foreground),
     (GetPrivateUserInfoResponse, Foreground),
     (GetChannelMembers, Foreground),
-    (GetChannelMembersResponse, Foreground)
+    (GetChannelMembersResponse, Foreground),
+    (GetChannelBuffer, Foreground),
+    (GetChannelBufferResponse, Foreground)
 );
 
 request_messages!(
@@ -315,6 +317,7 @@ request_messages!(
     (UpdateParticipantLocation, Ack),
     (UpdateProject, Ack),
     (UpdateWorktree, Ack),
+    (GetChannelBuffer, GetChannelBufferResponse)
 );
 
 entity_messages!(