[vello_cpu] reset transforms when resetting the RenderContext (#1054)

Small change, but I think it's intended that all state resets when
calling `.reset` on the RenderContext.

This change adds resetting of the `transform` and `paint_transform` when
`reset` is called.

Author: ajakubowicz-canva

sparse_strips/vello_cpu/src/render.rs

@@ -333,6 +333,8 @@ impl RenderContext {
     pub fn reset(&mut self) {
         self.dispatcher.reset();
         self.encoded_paints.clear();
+        self.reset_transform();
+        self.reset_paint_transform();
     }
 
     /// Flush any pending operations.