test(nodes): add OGG round-trip test for SymphoniaOggDemuxerNode

[staging-devin-ai-integration]

Context

PR #505 added OGG mux→demux round-trip tests using OggDemuxerNode, but the default feature set registers SymphoniaOggDemuxerNode when the symphonia feature is enabled (which it is by default).

Suggested change

Add a feature-gated test that instantiates SymphoniaOggDemuxerNode when #[cfg(feature = "symphonia")] is active, exercising the demuxer implementation most builds actually expose.

Origin

Identified by automated review on #505.