Ray-caster: add a third test sphere

This helps confirm that the generalized depth-sorting is working.

app-proto/inversive-display/src/main.rs

@@ -211,7 +211,7 @@ fn main() {
                 )
                 input(
                     type="range",
-                    max=3.0,
+                    max=5.0,
                     step=1.0,
                     bind:valueAsNumber=layer_threshold
                 )