Replace double with float, optimize calculation

Marlin/src/libs/vector_3.cpp

@@ -69,7 +69,7 @@ vector_3 vector_3::get_normal() {
 float vector_3::get_length() { return SQRT(sq(x) + sq(y) + sq(z)); }
 
 void vector_3::normalize() {
-  const float inv_length = 1.0 / get_length();
+  const float inv_length = RSQRT(sq(x) + sq(y) + sq(z));
   x *= inv_length;
   y *= inv_length;
   z *= inv_length;