feat(gst): enhance GStreamer integration with new modules and improved API

This commit introduces significant enhancements to the GStreamer integration by:
- Adding new modules for bins, caps, elements, pads, and plugins
- Implementing a more ergonomic API with helper methods like play(), pause(), ready()
- Adding support for various GStreamer plugins including app, autodetect, playback, and videoconvertscale
- Improving error handling with better context attachment
- Updating dependencies to latest versions including gstreamer-video 0.24.4
- Refactoring existing code to use modern Rust patterns and features

gst/src/plugins/app.rs

@@ -0,0 +1,2 @@
+pub mod appsink;
+pub use appsink::*;