Make BSpline matrix an expression

Assembly analysis shows that using an expression instead of applying the
div 6.0 operation using an iterator produces smaller and probably more
efficient code. The division by 6.0 was left in the matrix on all values
to explicitly show that all values are divided by it. Manually
simplifying some values doesn't result in any difference in the compiled code.
Godbolt: https://godbolt.org/z/MMfMhnMsq

crates/bevy_math/src/cubic_splines.rs

@@ -280,17 +280,13 @@ impl<P: Point> CubicBSpline<P> {
 impl<P: Point> CubicGenerator<P> for CubicBSpline<P> {
     #[inline]
     fn to_curve(&self) -> CubicCurve<P> {
-        let mut char_matrix = [
-            [1.0, 4.0, 1.0, 0.0],
-            [-3.0, 0.0, 3.0, 0.0],
-            [3.0, -6.0, 3.0, 0.0],
-            [-1.0, 3.0, -3.0, 1.0],
+        let char_matrix = [
+            [1.0 / 6.0, 4.0 / 6.0, 1.0 / 6.0, 0.0 / 6.0],
+            [-3.0 / 6.0, 0.0 / 6.0, 3.0 / 6.0, 0.0 / 6.0],
+            [3.0 / 6.0, -6.0 / 6.0, 3.0 / 6.0, 0.0 / 6.0],
+            [-1.0 / 6.0, 3.0 / 6.0, -3.0 / 6.0, 1.0 / 6.0],
         ];
 
-        char_matrix
-            .iter_mut()
-            .for_each(|r| r.iter_mut().for_each(|c| *c /= 6.0));
-
         let segments = self
             .control_points
             .windows(4)