Only process input callbacks for active controllers

This is cleaner and easier to understand for user applications:

- Controllers process input only when active
- This avoids sudden jumps upon activation due to some values from
  earlier callbacks.
- Controllers don't spam `NaN` warnings when inactive and working with
  fake hardware.

cartesian_controller_base/include/cartesian_controller_base/cartesian_controller_base.h

@@ -176,6 +176,13 @@ class CartesianControllerBase : public controller_interface::ControllerInterface
     return false;
   }
 
+  /**
+   * @brief Helper method to check the controller's state during input callbacks
+   *
+   * @return True if the controller is active, false otherwise
+   */
+  bool isActive() const {return m_active;};
+
   KDL::Chain m_robot_chain;
 
   std::shared_ptr<KDL::TreeFkSolverPos_recursive> m_forward_kinematics_solver;

cartesian_force_controller/src/cartesian_force_controller.cpp

@@ -209,6 +209,11 @@ void CartesianForceController::setFtSensorReferenceFrame(const std::string & new
 void CartesianForceController::targetWrenchCallback(
   const geometry_msgs::msg::WrenchStamped::SharedPtr wrench)
 {
+  if (!this->isActive())
+  {
+    return;
+  }
+
   if (std::isnan(wrench->wrench.force.x) || std::isnan(wrench->wrench.force.y) ||
       std::isnan(wrench->wrench.force.z) || std::isnan(wrench->wrench.torque.x) ||
       std::isnan(wrench->wrench.torque.y) || std::isnan(wrench->wrench.torque.z))
@@ -230,6 +235,11 @@ void CartesianForceController::targetWrenchCallback(
 void CartesianForceController::ftSensorWrenchCallback(
   const geometry_msgs::msg::WrenchStamped::SharedPtr wrench)
 {
+  if (!this->isActive())
+  {
+    return;
+  }
+
   if (std::isnan(wrench->wrench.force.x) || std::isnan(wrench->wrench.force.y) ||
       std::isnan(wrench->wrench.force.z) || std::isnan(wrench->wrench.torque.x) ||
       std::isnan(wrench->wrench.torque.y) || std::isnan(wrench->wrench.torque.z))

cartesian_motion_controller/src/cartesian_motion_controller.cpp

@@ -193,6 +193,11 @@ ctrl::Vector6D CartesianMotionController::computeMotionError()
 void CartesianMotionController::targetFrameCallback(
   const geometry_msgs::msg::PoseStamped::SharedPtr target)
 {
+  if (!this->isActive())
+  {
+    return;
+  }
+
   if (std::isnan(target->pose.position.x) || std::isnan(target->pose.position.y) ||
       std::isnan(target->pose.position.z) || std::isnan(target->pose.orientation.x) ||
       std::isnan(target->pose.orientation.y) || std::isnan(target->pose.orientation.z) ||