Add flat mesh slots for multi-mesh raycasts

[ooctipus]

Summary

• Add a flat per-environment mesh-slot Warp kernel for dynamic multi-mesh raycasts.
• Switch multi-mesh raycaster and camera launches from rectangular padded tables to compact slots.
• Update ClonePlan integration coverage to assert heterogeneous slot counts without USD object clones.

Test plan

• ./isaaclab.sh -p -m pytest source/isaaclab/test/sensors/test_ray_caster_integration.py::test_multi_mesh_consumes_clone_plan_without_usd_object_clones -q
• ./isaaclab.sh -p -m pytest source/isaaclab/test/sensors/test_multi_mesh_ray_caster_camera.py -q
• ./isaaclab.sh -p -m pytest source/isaaclab/test/sensors/test_ray_caster_integration.py::test_update_mesh_transforms_non_identity_offset -q
• ./isaaclab.sh -f

Made with Cursor

[ooctipus]

Superseded by upstream develop PR: isaac-sim#5531