Add typing indicator support in ChatView

[subhan9090]

This PR adds support for displaying a typing indicator in the ChatView when other users are typing. Key changes include:

Changes made:

ChatViewListAdapter

Added TYPING message type support.

Implemented addTypingIndicator(String sender) and removeTypingIndicator(String sender) methods for safely adding/removing typing indicators.

Ensured all list modifications and notifyDataSetChanged() calls occur on the UI thread using ListView.post().

Fixed getViewTypeCount() to return 3 (SENT, RECEIVED, TYPING), preventing ArrayIndexOutOfBoundsException.

ChatView

Added showTypingIndicator(String sender) and hideTypingIndicator(String sender) methods as a clean interface to manage typing indicators.

Supports multiple users typing concurrently without crashing.

Maintains existing message functionality intact.

Benefits:

Typing indicators now appear and disappear safely for each sender.

Fully compatible with existing messages.

Eliminates ArrayIndexOutOfBoundsException caused by incorrect view type count.

Usage:

chatView.showTypingIndicator("Alice");
chatView.hideTypingIndicator("Alice");