[Feature Request]: Display media outputs (image/audio/video/3D) directly on subgraph nodes

### Is there an existing issue for this?

- [x] I have searched the existing issues and checked the recent builds/commits

### What would your feature do?

Enable subgraph nodes to display media outputs (images, audio waveforms, video previews, 3D models) directly on the subgraph node itself in the parent graph view, similar to how SaveImage/PreviewImage nodes display their outputs. This would eliminate the need to connect subgraph outputs to separate preview/save nodes just to see the results.

Currently, when a subgraph outputs media content, users must:
1. Connect the subgraph output to a SaveImage/PreviewImage/SaveAudio node
2. Execute the workflow to see the output
3. This creates additional nodes and connections that clutter the workflow

With this feature, subgraphs that output media types would automatically display previews on the subgraph node itself, making workflows cleaner and providing immediate visual feedback.

### Proposed workflow

1. Create a subgraph that outputs an image/audio/video/3D model
2. In the parent graph, the subgraph node automatically detects media-type outputs
3. The subgraph node displays a preview of the media directly on the node:
- For images: Show thumbnail preview (similar to PreviewImage)
- For audio: Show waveform visualization
- For video: Show first frame or animated preview
- For 3D models: Show 3D preview (similar to Load3D nodes)
4. Preview updates automatically when the subgraph executes
5. Optional: Add a setting to toggle preview display on subgraph nodes

### Additional information

This feature would significantly improve the user experience when working with subgraphs that process media content. It would:

- Reduce workflow clutter by eliminating unnecessary preview nodes
- Provide immediate visual feedback for subgraph outputs
- Make subgraphs more self-contained and easier to understand at a glance
- Align with the existing behavior of nodes like SaveImage that show their outputs directly

The implementation could leverage existing preview mechanisms used by SaveImage, PreviewImage, SaveAudio, and Load3D nodes. The subgraph node would need to:
1. Detect output slot types that correspond to media formats
2. Subscribe to execution results for those outputs
3. Render appropriate preview widgets on the node

This would be particularly useful for subgraphs that perform image processing, audio manipulation, or 3D transformations where seeing the output is essential for workflow development.

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-4563-Feature-Request-Display-media-outputs-image-audio-video-3D-directly-on-subgraph-n-23e6d73d3650817193c8ceee40b15fc0) by [Unito](https://www.unito.io)