[wpimath] Replace Speeds with Velocities (#8479)

I left "free speed" alone since that's the technical term for it. In
general, velocity is a vector quantity, and speed is a magnitude (i.e.,
a strictly positive value).

This PR also replaces the speed verbiage in MotorController with duty
cycle.

Fixes #8423.

robotpyExamples/UnitTest/constants.py

@@ -10,7 +10,7 @@ class IntakeConstants:
 
     kPistonFwdChannel = 0
     kPistonRevChannel = 1
-    kIntakeSpeed = 0.5
+    kIntakeVelocity = 0.5
 
 
 kJoystickIndex = 0

robotpyExamples/UnitTest/robot.py

@@ -27,7 +27,7 @@ class MyRobot(wpilib.TimedRobot):
         """This function is called periodically during operator control."""
         # Activate the intake while the trigger is held
         if self.joystick.getTrigger():
-            self.intake.activate(constants.IntakeConstants.kIntakeSpeed)
+            self.intake.activate(constants.IntakeConstants.kIntakeVelocity)
         else:
             self.intake.activate(0)
 

robotpyExamples/UnitTest/subsystems/intake.py

@@ -26,9 +26,9 @@ class Intake:
         self.piston.set(wpilib.DoubleSolenoid.Value.kReverse)
         self.motor.set(0)  # turn off the motor
 
-    def activate(self, speed: float) -> None:
+    def activate(self, velocity: float) -> None:
         if self.isDeployed():
-            self.motor.set(speed)
+            self.motor.set(velocity)
         else:  # if piston isn't open, do nothing
             self.motor.set(0)