[Feature] Allows to turn on/off batch (links/dofs) info

[zswang666]

trafficstars

In the rigid solver option, there are batch_links_info and batch_dofs_info. If either is set to True, in the rigid solver, we introduce additional batch dimension (like in links_state or dofs_state). If they are both set to False, the built kernels in the solver should resemble those from the original code -- w/o the batch dimension.

An example is added in examples/rigid/set_phys_attr.py, which demonstrates how to set kp, kv, force range, armature, stiffness, invweight, damping for dofs and inertial mass, and invweight for links.

Related issues: https://github.com/Genesis-Embodied-AI/Genesis/issues/70, https://github.com/Genesis-Embodied-AI/Genesis/issues/120