Travel speculation (#173) and Aether 0.809.0

[nicolas-maman]

• WorldDef.enable_travel_speculation (and physics_world.enable_travel_speculation), off by default so the reference's results and the golden trace stay the same. When on, every contact keeps speculative points out to the pair's travel over the step, dynamic pairs included. That is what enable_kinematic_speculation (A kinematic body travelling past the speculative distance in a step finds slow dynamic bodies already inside it: a strike's first frame #167) does for a kinematic body's contacts. A moving body's fat bounds also cover its next step, a fast body's after its continuous sweep included, so the pair exists in time.
  • Why: a 1.2 t dynamic car at 6.5 to 7 m/s moves 11 cm a step. That's under the reference's continuous threshold (half its extent), so the light bodies it struck were found 5 to 8 cm inside it on the first frame.
  • tests/test_edge_cases: a ball or a 6 cm limb struck by a dynamic 1200 kg box at 7 m/s is under 1 cm deep, against 6 cm or more without the option. At 20 m/s (past the fast threshold) also under 1 cm. Off by default, and a world turns it on.
  • Recorded as OP_ENABLE_TRAVEL_SPECULATION (test_recording's every-op check now covers 162) and kept in snapshots (SNAPSHOT_VERSION 5).
  • In ae3d's plaza the seconds a struck figure's limbs spend inside the car went from 6.9 to 0.9 over eight seeds.
• Aether 0.809.0, the latest release (aeb v0.326 is already the latest). The whole gate passes on it locally, the golden trace bit for bit.

Closes #173.