Function handle_changes 

pub async fn handle_changes<O: JmapObject, B: JmapBackend>(
    backend: &B,
    args: Value,
) -> Result<(Value, Vec<Invocation>), JmapError>

Generic */changes handler (RFC 8620 §5.2).

Returns the standard changes response including updatedProperties: null (the server does not track which individual properties changed).