Impl Default for a few structs

src/geometry/broad_phase_multi_sap/broad_phase.rs

@@ -116,6 +116,12 @@ pub struct BroadPhase {
     reporting: HashMap<(u32, u32), bool>, // Workspace
 }
 
+impl Default for BroadPhase {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl BroadPhase {
     /// Create a new empty broad-phase.
     pub fn new() -> Self {

src/geometry/broad_phase_multi_sap/sap_proxy.rs

@@ -87,6 +87,12 @@ pub struct SAPProxies {
     pub first_free: SAPProxyIndex,
 }
 
+impl Default for SAPProxies {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl SAPProxies {
     pub fn new() -> Self {
         Self {