v3.12.0

A planning clearance is affordable: the native MuJoCo validator collides only the pairs that can change a decision
(#254), so margins on an environment full of resting objects no longer multiply the cost of a check.

Changed

• The native MuJoCo validator collides only the pairs that can change a decision (#254): pairs involving the arm or
  a held object. Resting objects are no longer collided against their supports or each other, so a planning margin
  on the environment stays cheap.
  • Decisions and contact lists are unchanged: the corpus test compares every contact (bodies, geoms, distance,
    kind, order) with a full mj_collision, at margin 0 and 5 mm, with and without a held object.
  • tools/collision_benchmark.py reports the per-check time, all pairs against the filtered pairs, at 0 and
    5 mm on a table of resting cans.