perf: migrate MotrixSim writes to batched compile_write FFI plan

[wlgys8]

Closes #20

Summary

• upgrade motrixsim to 0.10.1.dev123565, whose compile_write supports compile-time reset and forward_kinematic flags
• semantic writes (ctrl targets, body pose/velocities, kp/damping/mass/com/friction overrides, mocap poses) compile into one native WritePlan; each execute scatters in a single FFI call, applies the native reset first when compiled with reset=True, and refreshes kinematics at most once
• mocap pose declarations expand into per-body interleaved BodyPosition/BodyRotation fields; buffer(name) synthesizes the neutral (N, B, 7) layout as one zero-copy slice, so consumers are unchanged
• dof-channel writes keep the numpy scatter path but land through the explicit set_dof_pos/set_dof_vel setters: SceneData property projections are read-only copies, so in-place patches never reached the sim state
• keep compile-time conflict detection for dof and ctrl targets with the existing error messages; native duplicate-channel rejection covers the override fields
• drop _MultiTargetOp (unused after the migration) and the post-reset op branch (all remaining numpy ops fold into the reset state)

Test plan

• full workspace suite: 871 passed
• prek run clean on changed files
• smoke: cartpole skrl training, shadow-hand / go2 / stewart / manipulator envs step loops