feat(chat): implement sequence-based unread count tracking

Introduce a new mechanism for tracking read positions using message
sequences (hasReadSeq), similar to OpenIM, to allow for O(1) unread
count calculations.

- Implement `UserReadSeq` caching in Redis with Lua scripts to prevent
  sequence regression (ensuring updates only occur if the new sequence
  is greater than the current one).
- Update `ConversationCache` to support sequence-based unread count
  computation (`maxSeq - hasReadSeq`).
- Refactor `MessageRepository` to use conditional updates for
  `last_read_seq` in the database.
- Update `ChatService` to automatically update the sender's read
  sequence when sending a message.
- Optimize `MarkAsRead` logic to update both database and Redis
  sequence caches and refine notification targets for private vs
  group chats.
- Update `jpush` client to use pointer types for boolean fields to
  properly handle optional values in JSON.

internal/pkg/jpush/client.go

@@ -93,8 +93,8 @@ type IOSNotif struct {
 	Alert            any            `json:"alert,omitempty"`
 	Sound            any            `json:"sound,omitempty"`
 	Badge            string         `json:"badge,omitempty"`
-	MutableContent   bool           `json:"mutable-content,omitempty"`
-	ContentAvailable bool           `json:"content-available,omitempty"`
+	MutableContent   *bool          `json:"mutable-content,omitempty"`
+	ContentAvailable *bool          `json:"content-available,omitempty"`
 	Category         string         `json:"category,omitempty"`
 	ThreadID         string         `json:"thread-id,omitempty"`
 	Extras           map[string]any `json:"extras,omitempty"`