Fix notes unread status (#7643)

1. The client-side comparison was wrong
2. The server never told the client about the version it remembered
3. The server generated broken timestamps in some cases

Release Notes:

- Fixed the notes/chat appearing as unread too often

**or**

- N/A

crates/collab/src/db.rs

@@ -587,6 +587,9 @@ pub struct ChannelsForUser {
     pub channels: Vec<Channel>,
     pub channel_memberships: Vec<channel_member::Model>,
     pub channel_participants: HashMap<ChannelId, Vec<UserId>>,
+
+    pub observed_buffer_versions: Vec<proto::ChannelBufferVersion>,
+    pub observed_channel_messages: Vec<proto::ChannelMessageId>,
     pub latest_buffer_versions: Vec<proto::ChannelBufferVersion>,
     pub latest_channel_messages: Vec<proto::ChannelMessageId>,
 }