A character component: a moving, aiming, reacting person in a few lines #903

Setting up one figure on the animation pipeline takes too much: the showcase's figure on a stick is 96 lines and 56 calls across seven modules (figure, animator, clips, retarget, ikrig, mover, pose), with the clip preparation (straighten, loop cut, crop about the move) done by hand. Beside the pipeline, older modules still do parts of the same job (anim, feet, lookat, locomotion, idle, posing, ik, handover, and motion's own feet).

Wanted: one component, the way Unity's Animator plus a CharacterController reads, with defaults that are right for a person:

hero = character.humanoid(e, "Hero", "people/adventurer.glb", character.gaits("100style/neutral"))
character.move(hero, velocity, facing)      // every frame, from the game
character.aim(hero, target)
character.hit(hero, bone, point, impulse)   // physical reaction, then back to the animation

• Locomotion out of the box: idle, starts and stops by distance, a 2D blend of the gaits, turns on the spot in steps, motion matching where a database is given.
• Feet, look and aim IK on by default, held to the numbers test_anim_pipeline and test_ik_constraints already measure.
• States, takes and transitions declarable as data (a file), not only as calls.
• Everything underneath still reachable for a game that wants it.
• The overlapping older modules retired behind it (with M6 migration onto the animation pipeline; old writers retired #860).

Done when the showcase's figures are each set up in a few lines through it, the README's animation example is the real code, and every check in test_anim_pipeline and test_ik_constraints holds through the component.