wip: foregin eq from comparapable comp type.

This commit adds the framework for "comparable components". This allows
complete sealing of bump-allocated properties types, and a comparison method
that performs a "safe" cast without transmute. This lets us completely erase types
but still be able to perform partialeq over render frames

packages/core/examples/nested.rs

@@ -17,7 +17,7 @@ static Header: FC<()> = |ctx, props| {
             .child(VNode::Component(VComponent::new(
                 Bottom,
                 //
-                (),
+                &mut (),
             )))
             .finish()
     })