Explicitly specify actdim on PID plugin actuators, to allow them to be used with keyframes.

Support actdim attribute on plugin actuators.

Remove the actuator_actdim callback. This callback leads to crashes when loading keyframes for models that have a stateful plugin.

PiperOrigin-RevId: 650649505
Change-Id: I40d1994d02ae4e20ce631b2702a984766cf2628e

plugin/actuator/pid.h

@@ -52,9 +52,6 @@ class Pid {
   // Returns the number of state variables for the plugin instance
   static int StateSize(const mjModel* m, int instance);
 
-  // Returns the number of activation variables for the plugin instance
-  static int ActDim(const mjModel* m, int instance, int actuator_id);
-
   // Resets the C++ Pid instance's state.
   // plugin_state is a C array pointer into mjData->plugin_state, with a size
   // equal to the value returned from StateSize.
@@ -76,6 +73,9 @@ class Pid {
  private:
   Pid(PidConfig config, std::vector<int> actuators);
 
+  // Returns the expected number of activation variables for the instance.
+  static int ActDim(const mjModel* m, int instance, int actuator_id);
+
   struct State {
     mjtNum previous_ctrl = 0;
     // if using slew rate limits, mjData.act will contain an activation variable