Add linescan plugin for line scan camera simulation

- New plugin extracts single row/column from frames and builds line scan image
- Supports horizontal mode (extract row, stack vertically)
- Supports vertical mode (extract column, stack horizontally)
- Configurable line index and output size
- Proper caps negotiation with fixate_caps implementation
- Updated build system to include linescan plugin
- Added comprehensive README with usage examples

gst/CMakeLists.txt

@@ -5,6 +5,7 @@ endif (OPENCV_FOUND)
 add_subdirectory (bayerutils)
 add_subdirectory (extractcolor)
 add_subdirectory (intervalometer)
+add_subdirectory (linescan)
 
 if (ENABLE_KLV)
   add_subdirectory (klv)