feat(core): implement channel unreads model

closes #269

crates/core/models/src/v0/channel_unreads.rs

@@ -0,0 +1,27 @@
+auto_derived!(
+    /// Channel Unread
+    pub struct ChannelUnread {
+        /// Composite key pointing to a user's view of a channel
+        #[serde(rename = "_id")]
+        pub id: ChannelCompositeKey,
+
+        /// Id of the last message read in this channel by a user
+        #[cfg_attr(feature = "serde", serde(skip_serializing_if = "Option::is_none"))]
+        pub last_id: Option<String>,
+        /// Array of message ids that mention the user
+        #[cfg_attr(
+            feature = "serde",
+            serde(skip_serializing_if = "Vec::is_empty", default)
+        )]
+        pub mentions: Vec<String>,
+    }
+
+    /// Composite primary key consisting of channel and user id
+    #[derive(Hash)]
+    pub struct ChannelCompositeKey {
+        /// Channel Id
+        pub channel: String,
+        /// User Id
+        pub user: String,
+    }
+);

crates/core/models/src/v0/mod.rs

@@ -1,5 +1,6 @@
 mod bots;
 mod channel_invites;
+mod channel_unreads;
 mod channel_webhooks;
 mod channels;
 mod files;
@@ -9,6 +10,7 @@ mod users;
 
 pub use bots::*;
 pub use channel_invites::*;
+pub use channel_unreads::*;
 pub use channel_webhooks::*;
 pub use channels::*;
 pub use files::*;