Added command_levels_vel function for curriculum-based velocity command adjustment

[fan-ziqi]

Description

Added command_levels_vel function for curriculum-based velocity command adjustment, increasing the command range when the robot's tracking reward exceeds 80% of the maximum.

Modify from the update_command_curriculum() function in legged_gym

    def update_command_curriculum(self, env_ids):
        """ Implements a curriculum of increasing commands

        Args:
            env_ids (List[int]): ids of environments being reset
        """
        # If the tracking reward is above 80% of the maximum, increase the range of commands
        if torch.mean(self.episode_sums["tracking_lin_vel"][env_ids]) / self.max_episode_length > 0.8 * self.reward_scales["tracking_lin_vel"]:
            self.command_ranges["lin_vel_x"][0] = np.clip(self.command_ranges["lin_vel_x"][0] - 0.1, -self.cfg.commands.max_curriculum, 0.)
            self.command_ranges["lin_vel_x"][1] = np.clip(self.command_ranges["lin_vel_x"][1] + 0.1, 0., self.cfg.commands.max_curriculum)
            self.command_ranges["lin_vel_y"][0] = np.clip(self.command_ranges["lin_vel_y"][0] - 0.1, -self.cfg.commands.max_curriculum, 0.)
            self.command_ranges["lin_vel_y"][1] = np.clip(self.command_ranges["lin_vel_y"][1] + 0.1, 0., self.cfg.commands.max_curriculum)

Usage:

@configclass
class CurriculumCfg:
    """Curriculum terms for the MDP."""

    terrain_levels = CurrTerm(func=mdp.terrain_levels_vel)

    command_levels = CurrTerm(func=mdp.command_levels_vel, params={
        "reward_term_name": "track_lin_vel_xy_exp",
        "max_curriculum": 1.5,
    })

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

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