Preserve Search State and Keyword in CometChatSearch

Introduce built-in state persistence support for the CometChatSearch component in the Flutter UI Kit so that previously entered search keywords and search results are retained when users navigate away from and reopen the search screen during the same app session. Currently, the search state resets completely upon reopening the component, forcing users to re-enter search queries and repeat the search process. This behavior negatively impacts usability, especially in workflows involving frequent navigation between conversations and search results. Providing automatic state retention or exposing properties/callbacks to preserve and restore the search context would align the component with modern search UX standards, improve user experience, and reduce the need for custom state-management implementations.