Backtracking line search for SDF collisions.

Increased tolerance above zero in nutbolt.xml since now the two parts lock otherwise. Measured speedup of 2x in this example.

This solves the issue of scale-dependent step sizes. Tested on gears with 10cm diameter and 2cm thickness.

PiperOrigin-RevId: 584009449
Change-Id: Ied2f62dbbbc592470b91cf910f3553802a57c752

model/plugin/sdf/nutbolt.xml

@@ -8,7 +8,7 @@
     </plugin>
     <plugin plugin="mujoco.sdf.bolt">
       <instance name="bolt">
-        <config key="radius" value="0.26"/>
+        <config key="radius" value="0.255"/>
       </instance>
     </plugin>
   </extension>
@@ -30,7 +30,7 @@
     </mesh>
   </asset>
 
-  <option sdf_iterations="15" sdf_initpoints="60"/>
+  <option sdf_iterations="10" sdf_initpoints="20"/>
 
   <default>
     <geom solref="0.01 1" solimp=".95 .99 .0001" friction="0.01"/>