Fix clippy and enable clippy on CI

src/dynamics/coefficient_combine_rule.rs

@@ -7,10 +7,11 @@ use crate::math::Real;
 /// Each collider has its combination rule of type
 /// `CoefficientCombineRule`. And the rule
 /// actually used is given by `max(first_combine_rule as usize, second_combine_rule as usize)`.
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Default, Copy, Clone, Debug, PartialEq, Eq)]
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
 pub enum CoefficientCombineRule {
     /// The two coefficients are averaged.
+    #[default]
     Average = 0,
     /// The smallest coefficient is chosen.
     Min,
@@ -20,12 +21,6 @@ pub enum CoefficientCombineRule {
     Max,
 }
 
-impl Default for CoefficientCombineRule {
-    fn default() -> Self {
-        CoefficientCombineRule::Average
-    }
-}
-
 impl CoefficientCombineRule {
     pub(crate) fn combine(coeff1: Real, coeff2: Real, rule_value1: u8, rule_value2: u8) -> Real {
         let effective_rule = rule_value1.max(rule_value2);