Fix clippy and enable clippy on CI

src/dynamics/joint/motor_model.rs

@@ -1,23 +1,18 @@
 use crate::math::Real;
 
 /// The spring-like model used for constraints resolution.
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Default, Copy, Clone, Debug, PartialEq, Eq)]
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
 pub enum MotorModel {
     /// The solved spring-like equation is:
     /// `acceleration = stiffness * (pos - target_pos) + damping * (vel - target_vel)`
+    #[default]
     AccelerationBased,
     /// The solved spring-like equation is:
     /// `force = stiffness * (pos - target_pos) + damping * (vel - target_vel)`
     ForceBased,
 }
 
-impl Default for MotorModel {
-    fn default() -> Self {
-        MotorModel::AccelerationBased
-    }
-}
-
 impl MotorModel {
     /// Combines the coefficients used for solving the spring equation.
     ///