Pitivi Timeline Ruler: Native GTK4/Rust Rewrite

The Pitivi timeline ruler currently relies on a legacy Python implementation using GTK3 and the Cairo drawing model. As Pitivi updates to a modern GTK4 native structure, the CPU-heavy Cairo draw calls are becoming a bottleneck for rendering time markers and frames at varying levels of zoom. This project will rewrite the ruler as a standalone, native GTK4 widget using Rust and ‘gtk-rs’. By moving away from Cairo and utilizing GTK4’s hardware acceleration via ‘GtkSnapshot’ and Render Nodes, the new ruler will be significantly more performant and memory-safe. Following a modular design philosophy, the widget will be built independently with a robust GObject API before being integrated into Pitivi’s existing Python and GStreamer Editing Services (GES) infrastructure using GObject introspection.