New contacts are bouncy, old are resting

If a contact is new (previous impluse = 0), then we treat it as bouncy (respecting restitution).
If the contact is old we treat it as resting.

Exceptions for restitutions <=0 and >= 1.

src/geometry/contact_pair.rs

@@ -128,6 +128,22 @@ pub struct SolverContact {
     pub data: ContactData,
 }
 
+impl SolverContact {
+    /// Should we treat this contact as a bouncy contact?
+    /// If `true`, use [`Self::restitution`].
+    pub fn is_bouncy(&self) -> bool {
+        let is_new = self.data.impulse == 0.0;
+        if is_new {
+            // Treat new collisions as bouncing at first, unless we have zero restitution.
+            self.restitution > 0.0
+        } else {
+            // If the contact is still here one step later, it is now a resting contact.
+            // The exception is very high restitutions, which can never rest
+            self.restitution >= 1.0
+        }
+    }
+}
+
 impl Default for ContactManifoldData {
     fn default() -> Self {
         Self::new(