render: remove getters from Surface, reimplement buffer sharing with Send+Sync

src/render.rs

@@ -1,4 +1,3 @@
-use std::io;
 use rgb::Rgb;
 
 use crate::geometry::*;
@@ -35,13 +34,10 @@ pub trait Surfaces: Send + Sync {
 }
 
 pub trait Surface: Send + Sync {
-    fn with_shader<F: FnMut(&dyn Shader)>(&self, f: F);
     fn set_shader(&mut self, shader: Box<dyn Shader>);
     fn clear_shader(&mut self);
 
-    fn rect(&self) -> Rectangle<Virtual>;
     fn set_rect(&mut self, rect: &Rectangle<Virtual>);
-    fn opacity(&self) -> u8;
     fn set_opacity(&mut self, opacity: u8);
 }