Add octree support to MJX API.

Also, enable the touch sensor to use the octree SDF.

PiperOrigin-RevId: 783313462
Change-Id: I0032c2a7164f4770aa10a3612db3fd70bea954db

mjx/mujoco/mjx/_src/types.py

@@ -527,6 +527,9 @@ class ModelC(PyTreeNode):
   bvh_child: jax.Array
   bvh_nodeid: jax.Array
   bvh_aabb: jax.Array
+  oct_child: jax.Array
+  oct_aabb: jax.Array
+  oct_coeff: jax.Array
   geom_plugin: jax.Array
   light_bodyid: jax.Array
   light_targetbodyid: jax.Array
@@ -742,6 +745,8 @@ class Model(PyTreeNode):
   mesh_faceadr: np.ndarray
   mesh_bvhadr: np.ndarray
   mesh_bvhnum: np.ndarray
+  mesh_octadr: np.ndarray
+  mesh_octnum: np.ndarray
   mesh_graphadr: np.ndarray
   mesh_vert: np.ndarray
   mesh_face: np.ndarray