rsinter (intersink/intersrc) do not pass custom serialized events

Describe your issue

The intersink/intersrc elements forward various events both downstream and upstream. Custom downstream events are not passed, however.

Expected Behavior

I expect serialized custom events to pass between the elements for application support.

Observed Behavior

The intersink underlying appsink posts a log message that it received the event, however it is passed into the basesink class where it's destroyed.

Setup

• Operating System: Ubuntu 22.04
• Device: Computer
• gst-plugins-rs Version: 0.12.7
• GStreamer Version: 1.24.5
• Command line: Powershell

Steps to reproduce the bug

1. Establish a pair of pipelines such that there is an intersink and intersrc pair between the two.
2. Add a periodic task that inserts custom downstream events containing some arbitrary structure ahead of the intersink element in the first pipeline.
3. Add a downstream event probe after the intersrc element in the other pipeline to print custom events that have been received and log them.

None of the events produced by (2) will be logged by (3).

How reproducible is the bug?

Always.

Screenshots if relevant

Solutions you have tried

I added the following test, which fails on the push_event call.

#[test]
#[serial]
fn test_push_custom_event() {
    init();

    let mut hc = start_consumer("p");
    let (srcpad, _) = start_producer("p");

    assert!(
        srcpad.push_event(gst::event::CustomDownstream::new(
            gst::Structure::builder("MyEvent")
                .field("unsigned", 100u64)
                .build()
        ))
    );
    let event = hc.pull_event();
    assert!(event.is_ok());
}

I then tried modifying inter/src/streamproducer/mod.rs to call upon constructing a producer, since it appears the gst_utils::StreamProducer supports this interface with EOS being the only default message to forward:

producer.set_forward_events(vec![
    gst::EventType::Eos,
    gst::EventType::CustomDownstream,
]);

However, the above test still fails on push_event (returned false).

Related non-duplicate issues

Additional Information