Fix contact params estimation in fixed-base models

If the `model.physics_model.is_floating_base` is False, with the current version, the whole `W_p_CoM` variable is returned (`shape=(3,)`), but it should have `shape=()`

src/jaxsim/api/contact.py

@@ -164,14 +164,14 @@ def estimate_model_height(model: Model.JaxSimModel) -> jtp.Float:
         """"""
 
         zero_data = Data.JaxSimModelData.build(
-            model=model, soft_contacts_params=soft_contacts.SoftContactsParams()
+            model=model, soft_contacts_params=soft_contacts.SoftContactsParams()[2]
         )
 
         W_p_CoM = Model.com_position(model=model, data=zero_data)
 
         if model.physics_model.is_floating_base:
             W_pz_C = collidable_point_positions(model=model, data=zero_data)[:, -1]
-            return 2 * (W_p_CoM[2] - W_pz_C.min())
+            return 2 * (W_p_CoM - W_pz_C.min())
 
         return 2 * W_p_CoM