Handle rollout MuJoCo errors as warnings

[devshahofficial]

Summary

• add raise_on_error to rollout so existing strict error behavior remains the default
• when raise_on_error=False, intercept MuJoCo fatal errors during a rollout, fill the failed trajectory remainder from the current state and sensor data, and continue other batches
• document the new tolerant path and cover both single-threaded and threaded rollout behavior

Fixes #2704

Validation

• python3 -m py_compile python/mujoco/rollout.py python/mujoco/rollout_test.py
• built local MuJoCo, generated the Python sdist, built and installed a wheel from this checkout
• MUJOCO_GL=disable /tmp/mujoco-rollout-venv/bin/python -m pytest -q --pyargs mujoco.rollout_test (67 passed, 1 skipped)

[devshahofficial]

@haroonq @yuvaltassa this is now marked ready for review. Would one of you, or another active maintainer/contributor, be able to take a look when you have bandwidth? Happy to follow up on any requested changes or adjust the approach if there is a better direction.