Function start_owp_with

pub async fn start_owp_with(
    engine: Arc<Engine>,
    edit: impl FnOnce(&mut OwpConfig),
) -> (String, CancellationToken)

As start_owp, with the config open for editing first.

Tests for the resource limits set them far below their defaults, so that reaching one costs a few frames instead of megabytes. The listener is already bound; edit must not change OwpConfig::bind to a different address.