[Bug]: debug camera seems to be broken when env_separate_rigid=True

[Kashu7100]

Bug Description

The debug camera seems to be broken.

import genesis as gs
import torch

gs.init()
scene = gs.Scene(
    vis_options=gs.options.VisOptions(
        env_separate_rigid=True # this one 
    ),
    show_viewer=False
)
cam = scene.add_camera(
    pos=(1.5, 0., 1),
    lookat=(0., 0., 0.5),
    res=(720, 480),
    fov=80,
    GUI=False,
    debug=True, # this one 
)
scene.build(n_envs=1)

Steps to Reproduce

This works fine

import genesis as gs
import torch

gs.init()
scene = gs.Scene(
    show_viewer=False
)
cam = scene.add_camera(
    pos=(1.5, 0., 1),
    lookat=(0., 0., 0.5),
    res=(720, 480),
    fov=80,
    GUI=False,
    debug=True,
)
scene.build(n_envs=1)

This will trigger the issue

import genesis as gs
import torch

gs.init()
scene = gs.Scene(
    vis_options=gs.options.VisOptions(
        env_separate_rigid=True
    ),
    show_viewer=False
)
cam = scene.add_camera(
    pos=(1.5, 0., 1),
    lookat=(0., 0., 0.5),
    res=(720, 480),
    fov=80,
    GUI=False,
    debug=True,
)
scene.build(n_envs=1)

(the camera._pos is torch.Size([3]) but given envs_idx is (0,) and pos is torch.Size([1, 3]) at self._pos[envs_idx] = pos in L674 camera.py)

Expected Behavior

can use the debug camera without error.

Screenshots/Videos

No response

Relevant log output

Traceback (most recent call last):
  File "/home/kashu/research/Eden/tests/test_scene.py", line 40, in <module>
    env.build()
  File "/home/kashu/research/Genesis/genesis/utils/misc.py", line 140, in wrapper
    return method(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/kashu/research/Eden/eden/envs/base.py", line 167, in build
    self.scene.build(
  File "/home/kashu/research/Genesis/genesis/utils/misc.py", line 140, in wrapper
    return method(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/kashu/research/Genesis/genesis/engine/scene.py", line 819, in build
    self._visualizer.build()
  File "/home/kashu/research/Genesis/genesis/vis/visualizer.py", line 184, in build
    camera.build()
  File "/home/kashu/research/Genesis/genesis/vis/camera.py", line 193, in build
    self.set_pose(
  File "/home/kashu/research/Genesis/genesis/vis/camera.py", line 674, in set_pose
    self._pos[envs_idx] = pos
    ~~~~~~~~~^^^^^^^^^^
  File "/home/kashu/miniconda3/envs/genesis/lib/python3.12/site-packages/torch/utils/_device.py", line 103, in __torch_function__
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
RuntimeError: expand(torch.FloatTensor{[3]}, size=[]): the number of sizes provided (0) must be greater or equal to the number of dimensions in the tensor (1)

Environment

• OS: [e.g. Ubuntu 24.04, Windows 11 24H2]
• GPU/CPU [e.g. A100, RTX 4090, M3pr, Intel I9-9900k, Ryzen 5900x] (N/A if no GPU/CPU)
• GPU-driver version (N/A if no GPU)
• CUDA / CUDA-toolkit version (N/A if non-Nvidia)

Release version or Commit ID

0.3.6

Additional Context

No response