pybricks.common.Control: Fix scale doc.

Document it as an attribute instead of in the main docstring. This way we can choose where it shows up in the docs.

doc/main/motors.rst

@@ -25,6 +25,9 @@ the settings.
 .. autoclass:: pybricks._common.Control
     :no-members:
 
+    .. autoattribute:: pybricks._common.Control.scale
+      :annotation:
+
     .. rubric:: Status
 
     .. automethod:: pybricks._common.Control.done

src/pybricks/_common.py

@@ -90,13 +90,13 @@ class DCMotor:
 
 
 class Control:
-    """Class to interact with PID controller and settings.
+    """Class to interact with PID controller and settings."""
 
-        .. data:: scale
-
-            Scaling factor between the controlled integer variable
-            and the physical output. For example, for a single
-            motor this is the number of encoder pulses per degree of rotation.
+    scale = 1.0
+    """
+    Scaling factor between the controlled integer variable
+    and the physical output. For example, for a single
+    motor this is the number of encoder pulses per degree of rotation.
     """
 
     def limits(self, speed, acceleration, duty, torque):