perf: move MotrixSim write compiler onto native write plans

[wlgys8]

Summary

Migrate the MotrixSim write path onto batched native write programs: every declarative write compiles into a single native plan and execution is one native_program.execute call.

Supersedes #45 (same work, second-generation implementation rebased onto current main).

MotrixSim backend

• Migrate the compiler onto the batched compile_write FFI plan; reset/FK behavior is baked into the plan at compile time via SceneModel.compile_write(reset=, forward_kinematic=)
• Upgrade motrixsim to the official PyPI 0.10.1 release (was 0.10.1.dev124285 from the internal index); the internal motphys-dev index entry is dropped from pyproject.toml since release versions are published on PyPI
• Split the fused MocapPoseWrite (N,B,7) contract into separate position/rotation writes, both compiled to native BodyPosition/BodyRotation; _MultiTargetOp removed; four envs migrated
• JointPositionWrite/JointVelocityWrite compile to native BodyJointPosition/BodyJointVelocity joint-name sources
• Add neutral JointQuaternionWrite (xyzw, normalized on write) and JointAngularVelocityWrite from core/motphys-articulated-body#2106 (MR !1755); migrate peg-insert off the multi-DoF patch path

Core (backend-neutral)

• Rename MocapPositionWrite/MocapRotationWrite → KinematicBodyPositionWrite/KinematicBodyRotationWrite: "mocap" is an MJCF/MuJoCo asset concept and must not leak into the backend-neutral write vocabulary

Testing

• motrix_env_core + motrix_env_motrixsim test suites pass (56 tests)

[Copilot]

Copilot review overview

🔵 Needs a closer look

It is a broad refactor of the write vocabulary and reset lifecycle that swaps to a new native FFI (compile_write/mtx_write.*) whose behavior and quaternion conventions cannot be verified in this environment, warranting human review.

Review effort: Balanced
Findings: 2

Open (2)

• Rename dispatch labels to kinematic_body_* for consistency · New
• Remove dead _masked_rows helper after compiler API change · New

What changed in this PR

This PR migrates the MotrixSim backend's declarative write path onto batched native write programs. Every compiled write set now becomes a single SceneModel.compile_write(...) plan whose reset and forward‑kinematics behavior are baked in at compile time, and execution collapses to one native_program.execute FFI call. It also upgrades motrixsim from the internal dev build to the official PyPI 0.10.1, renames the backend‑neutral Mocap*Write vocabulary to KinematicBody*Write, splits the fused mocap pose write into separate position/rotation writes, and adds neutral JointQuaternionWrite/JointAngularVelocityWrite for ball joints (used to move peg‑insert off the multi‑DoF path). It fits into the framework's backend‑neutral core / simulator‑backend split by keeping the neutral write declarations while replacing the MotrixSim‑specific numpy scatter ops with native plans.

Changes:

• Replace numpy-scatter write ops (_DofChannelOp, _MultiTargetOp, _CtrlOp, reset patch ops) with a single native compile_write plan; drop DofPositionWrite/DofVelocityWrite.
• Rename MocapPositionWrite/MocapRotationWrite intent to neutral KinematicBodyPositionWrite/KinematicBodyRotationWrite, split fused pose writes, and add JointQuaternionWrite/JointAngularVelocityWrite; migrate 5 envs.
• Upgrade motrixsim to PyPI 0.10.1, dropping the internal motphys-dev index.

File	Description
motrix_env_core/​src/​motrix_env_core/​sim/​write.py	Removes Dof writes, renames mocap writes to kinematic-body, adds ball-joint writes + abstract hooks.
motrix_env_core/​src/​motrix_env_core/​sim/​__init__.py	Drops DofPositionWrite/DofVelocityWrite from re-exports and __all__.
motrix_env_motrixsim/​src/​motrix_env_motrixsim/​write_compiler.py	Rewrites compiler onto native compile_write plans; adds ball-joint/single-DoF/mocap validation.
motrix_env_motrixsim/​src/​motrix_env_motrixsim/​runtime.py	Drops masked_rows arg from compiler construction (leaves _masked_rows unused).
motrix_envs/​.../​shadow_hand_np.py, anymal_c_np.py, manipulator_np.py, bounce_ball_np.py	Split mocap pose writes into separate position/rotation kinematic-body writes.
motrix_envs/​.../​rm65_insert_peg/​insert_peg_np.py	Moves peg off multi-DoF free-joint writes onto per-quantity slide/ball joint writes.
motrix_env_motrixsim/​pyproject.toml, pyproject.toml, uv.lock	Upgrade motrixsim to PyPI 0.10.1; drop internal index.
motrix_env_motrixsim/​tests/​*, motrix_env_core/​tests/​*	Rework write-compiler/backend/dispatch tests; delete _MultiTargetOp test.

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