relax Send + Sync constraint on Renderables; remove 3 format calls from render loop

maybe render should have mutable access after all?

output/src/output.rs

@@ -21,13 +21,13 @@ pub trait Output: Send + Sync + Sized {
     #[inline] fn wh (&self) -> Self::Size { self.area().wh().into() }
 }
 /// Renderable with dynamic dispatch.
-pub trait Render<E: Output>: Send + Sync {
+pub trait Render<E: Output> {
     /// Compute layout.
     fn layout (&self, area: E::Area) -> E::Area;
     /// Write data to display.
     fn render (&self, output: &mut E);
     /// Perform type erasure, turning `self` into an opaque [RenderBox].
-    fn boxed <'a> (self) -> RenderBox<'a, E> where Self: Sized + 'a {
+    fn boxed <'a> (self) -> RenderBox<'a, E> where Self: Send + Sync + Sized + 'a {
         Box::new(self) as RenderBox<'a, E>
     }
 }
@@ -50,7 +50,7 @@ impl<'a, E: Output> Content<E> for RenderBox<'a, E> {
     //fn boxed <'b> (self) -> RenderBox<'b, E> where Self: Sized + 'b { self }
 }
 /// Opaque pointer to a renderable.
-pub type RenderDyn<'a, E> = dyn Render<E> + 'a;
+pub type RenderDyn<'a, E> = dyn Render<E> + Send + Sync + 'a;
 /// You can render from an opaque pointer.
 impl<'a, E: Output> Content<E> for &RenderDyn<'a, E> where Self: Sized {
     fn content (&self) -> impl Render<E> { self.deref() }
@@ -58,7 +58,7 @@ impl<'a, E: Output> Content<E> for &RenderDyn<'a, E> where Self: Sized {
     fn render (&self, output: &mut E) { Render::render(self.deref(), output) }
 }
 /// Composable renderable with static dispatch.
-pub trait Content<E: Output>: Send + Sync + Sized {
+pub trait Content<E: Output> {
     /// Return a [Render]able of a specific type.
     fn content (&self) -> impl Render<E> { () }
     /// Perform layout. By default, delegates to [Self::content].

output/src/thunk.rs

@@ -12,9 +12,9 @@ impl<E: Output, T: Render<E>, F: Fn()->T + Send + Sync> Content<E> for Thunk<E,
     fn content (&self) -> impl Render<E> { (self.1)() }
 }
 
-pub struct ThunkBox<'a, E: Output>(PhantomData<E>, Box<dyn Fn()->Box<dyn Render<E> + 'a> + Send + Sync + 'a>);
+pub struct ThunkBox<'a, E: Output>(PhantomData<E>, Box<dyn Fn()->RenderBox<'a, E> + Send + Sync + 'a>);
 impl<'a, E: Output> ThunkBox<'a, E> {
-    pub fn new (thunk: Box<dyn Fn()->Box<dyn Render<E> + 'a> + Send + Sync + 'a>) -> Self {
+    pub fn new (thunk: Box<dyn Fn()->RenderBox<'a, E> + Send + Sync + 'a>) -> Self {
         Self(Default::default(), thunk)
     }
 }