[Bug Report] Modifiers and history buffer cannot be used together in observation term

[ZiwenZhuang]

Describe the bug

Modifiers and history buffer cannot be used together in observation term.

Steps to reproduce

Setting any of the observation term with both history_length and class-based modifiers (e.g. Integrator) will lead to dimension mismatch error.

For example

from isaaclab.utils import IntegratorCfg

actions = ObsTerm(
    func=mdp.last_action,
    history_length=5,
    modifiers=[
        IntegratorCfg(dt=0.02),
    ],
)

Additional context

Running on IsaacLab 2.1.0

Checklist

• I have checked that there is no similar issue in the repo (required)
• I have checked that the issue is not in running Isaac Sim itself and is related to the repo

Acceptance Criteria

Add the criteria for which this task is considered done. If not known at issue creation time, you can add this once the issue is assigned.

• Fixing by moving observation_manager's history buffer initialization after the initialization of modifiers.

[RandomOakForest]

Thanks for posting this and adding the PR. The team will review.