feat: add pagination support for listRoots operation (#336)

- Add nextCursor field to ListRootsResult for cursor-based pagination
- Implement automatic pagination in McpAsyncServerExchange.listRoots()
 - Automatically fetches and combines all pages into single result
 - Refactor McpAsyncServerExchange.listRoots() to return Collections.unmodifiableList
- Update tests to verify pagination functionality

- Add test suite for McpAsyncServerExchange covering:
  - listRoots() pagination scenarios and edge cases
  - Logging notification with level filtering
  - Elicitation creation with various capabilities
  - Message creation with sampling capabilities
  - Error handling and validation scenarios
  - Verify sendNotification calls in logging notification tests
  - Verify sendRequest is never called when capabilities are missing

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>