Persistent data notifications from Rust API

Current state of data notifications in Rust API:

https://github.com/Vector35/binaryninja-api/blob/6e50ceda4e65e5952e59449fad4953ea6c5aaf37/rust/tests/data_notification.rs#L16-L33

The custom is of type DataNotificationHandle which is defined as:

https://github.com/Vector35/binaryninja-api/blob/ca0e32efb1e5b9eba157e9fd2eef178d9367c578/rust/src/data_notification.rs#L414-L421

This means that we are holding a strong reference to the view (for the purposes of dropping the data notification when custom is dropped) which inhibits the ability to leak the custom handle to persist the data notifications, we need to address this somehow to make using data notifications in Rust API more user friendly and less of a footgun.

One idea would be to provide an alternate register API that does not return a handle containing a strong reference to the view, or instead hold a weak reference to the view (but that is very difficult to do).

See this example for a motivating reason.

Start with rust/tests/data_notification.rs#L16-L33 and rust/src/data_notification.rs#L414-L421 to understand how DataNotificationHandle retains the view, then review the linked motivating example. Define and test a persistent-notification approach that avoids the current strong-reference limitation while preserving safe cleanup behavior.