Add filterexact and actearly options to MuJoCo.

When filterexact is a new dyntype which is just like the existing `filter`, but the activation state is integrated with exact integration, instead of simple Euler integration.

When actearly is specified on a general actuator, `qfrc_actuator` is computed using the next timestep's `act` value, instead of the current value.

PiperOrigin-RevId: 554438423
Change-Id: If901e4988fa6b518d6f3097f149770665a189a4b

unity/Runtime/Bindings/MjBindings.cs

@@ -250,8 +250,9 @@ public enum mjtDyn : int{
   mjDYN_NONE = 0,
   mjDYN_INTEGRATOR = 1,
   mjDYN_FILTER = 2,
-  mjDYN_MUSCLE = 3,
-  mjDYN_USER = 4,
+  mjDYN_FILTEREXACT = 3,
+  mjDYN_MUSCLE = 4,
+  mjDYN_USER = 5,
 }
 public enum mjtGain : int{
   mjGAIN_FIXED = 0,
@@ -2184,6 +2185,7 @@ public unsafe struct mjModel_ {
   public double* actuator_dynprm;
   public double* actuator_gainprm;
   public double* actuator_biasprm;
+  public byte* actuator_actearly;
   public double* actuator_ctrlrange;
   public double* actuator_forcerange;
   public double* actuator_actrange;