Add propeller spin direction

src/forces.zig

@@ -23,7 +23,7 @@ pub fn propThrust(attitude: vec3.QuatF64, p: drone.Propeller) struct { vec3.Vec3
     const drag_moment = vec3.Vec3F64.init(
         0,
         0,
-        p.moment_coefficient * p.angular_velocity * p.angular_velocity,
+        @intFromEnum(p.direction) * p.moment_coefficient * p.angular_velocity * p.angular_velocity,
     );
 
     return .{ force, vec3.vec3Add(force_moment, drag_moment) };
@@ -55,6 +55,7 @@ test "thrust is correct" {
         .angular_velocity = 100,
         .thrust_coefficient = 1,
         .moment_coefficient = 2,
+        .direction = constants.PropSpinDirection.cw,
     };
 
     const expected_thrust_mag = -100 * 100;