feat: adapt linescan scripts to use uv and proper rollover-based file saving

- Updated launch_with_signal.py with PEP 723 metadata for uv compatibility
- Added day/night mode presets with command-line arguments
- Implemented proper rollover-only file saving via Python/PIL callbacks
- Removed multifilesink from pipeline (was saving every frame incorrectly)
- Added funny auto-generated output directory names (e.g., fuzzy-photon)
- Updated rollover_example.py to follow same pattern with uv support
- Updated rollover_example.c to demonstrate signal detection without file saving
- Updated launch_with_capture.ps1 to remove incorrect multifilesink usage
- All scripts now save files ONLY on rollover events, not every frame
- Pipeline simplified: camera -> linescan -> display (files saved in callback)

gst/linescan/gstlinescan.h

@@ -78,6 +78,9 @@ struct _GstLinescan
 struct _GstLinescanClass
 {
   GstBaseTransformClass parent_class;
+
+  /* Signals */
+  void (*rollover) (GstLinescan *linescan, GstBuffer *buffer);
 };
 
 GType gst_linescan_get_type(void);