Fix SMPL humanoid qpos convention

[abcamiletto]

Summary

• convert SMPL humanoid axis-angle body pose to lowercase xyz Euler hinge coordinates for XML qpos
• parse SMPL humanoid XML hinge ranges and use them for qpos clipping

Notes

• No new tests added; existing expectations were updated for the XML qpos convention.
• SmplHumanoid uses the identity MuJoCo/model root frame, so the generic RigidBodyModel.to_qpos root conversion is not the source of the mismatch here.

Verification

• uv run ruff check src/body_models/robots/smpl_humanoid tests/test_smpl_humanoid.py tests/test_backend_consistency.py
• uv run ruff format --check src/body_models/robots/smpl_humanoid tests/test_smpl_humanoid.py tests/test_backend_consistency.py
• uv run --group dev --extra torch --extra jax ty check
• uv run --group dev --extra torch --extra jax -m pytest tests/test_backend_consistency.py tests/test_smpl_humanoid.py -q
• repro-style local comparison: mean abs qpos diff 2.45e-11, max abs qpos diff 3.73e-09