feat: expose rigid body force-at-position bindings

[luzhuang]

Summary

• Expose PxRigidBodyExt force-at-position helpers for world/local force and impulse use cases.
• Expose velocity-at-position helpers alongside the force helpers.
• Keep existing force mode semantics explicit: force helpers use eFORCE, impulse helpers use eIMPULSE, all with autowake=true.

Verification

• env -u PYTHONPATH -u CONDA_PYTHON_EXE EMSDK_QUIET=1 bash -lc "source /Users/wz/emsdk/emsdk_env.sh >/dev/null && ./build.sh"
• Built release and SIMD release wasm with default LTO configuration using emmake make -j1.
• Node smoke: PxRigidDynamic.prototype exposes addForceAtPos, local force/impulse helpers, and velocity-at-position helpers.