Fix terrain_out_of_bounds to return tensor instead of bool

[fan-ziqi]

Description

Fix terrain_out_of_bounds to return tensor instead of bool

Ensure the function always returns a PyTorch tensor (shape [num_envs]) rather than a Python boolean when terrain_type is "plane", preventing AttributeError in termination_manager.

Before:

Error executing job with overrides: []
Traceback (most recent call last):
  File "/home/ubuntu/workspaces/IsaacLab/source/isaaclab_tasks/isaaclab_tasks/utils/hydra.py", line 101, in hydra_main
    func(env_cfg, agent_cfg, *args, **kwargs)
  File "/home/ubuntu/workspaces/robot_lab/scripts/reinforcement_learning/rsl_rl/train.py", line 165, in main
    runner.learn(num_learning_iterations=agent_cfg.max_iterations, init_at_random_ep_len=True)
  File "/home/ubuntu/miniconda3/envs/lab/lib/python3.11/site-packages/rsl_rl/runners/on_policy_runner.py", line 206, in learn
    obs, rewards, dones, infos = self.env.step(actions.to(self.env.device))
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/workspaces/IsaacLab/source/isaaclab_rl/isaaclab_rl/rsl_rl/vecenv_wrapper.py", line 176, in step
    obs_dict, rew, terminated, truncated, extras = self.env.step(actions)
                                                   ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/miniconda3/envs/lab/lib/python3.11/site-packages/gymnasium/wrappers/common.py", line 393, in step
    return super().step(action)
           ^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/miniconda3/envs/lab/lib/python3.11/site-packages/gymnasium/core.py", line 327, in step
    return self.env.step(action)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/workspaces/IsaacLab/source/isaaclab/isaaclab/envs/manager_based_rl_env.py", line 204, in step
    self.reset_buf = self.termination_manager.compute()
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/workspaces/IsaacLab/source/isaaclab/isaaclab/managers/termination_manager.py", line 172, in compute
    rows = value.nonzero(as_tuple=True)[0]  # indexing is cheaper than boolean advance indexing
           ^^^^^^^^^^^^^
AttributeError: 'bool' object has no attribute 'nonzero'

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there