Change handling of "stale" data.

[jonnybergdahl]

Summary of Changes

The rt_data_stale property was added to separate data monitoring from connection management:

• Decoupled Health Check: The watchdog no longer uses data arrival to decide if it should reconnect. It now relies only on transport-level signals (WebSocket pings/timeouts).
• New rt_data_stale Property: Provides a boolean flag indicating if real-time data is older than 60 seconds, allowing users to monitor data flow independently.
• Modified rt_subscription_running: Now strictly reports if the WebSocket connection is active, preventing unnecessary reconnect cycles when data is simply delayed.
• Improved Stability: Reduces API load and prevents "reconnect storms" during periods of low data frequency or API instability.

[MartinHjelmare]

Side note: I have a branch that I plan to submit where I've removed the custom watchdog in favor of the builtin keep alive and ping-pong settings of the gql websocket.

Edit: See #401