Make wandb and lerobot optional across default callbacks and datasets

[james77777778]

Why

• wandb: Due to security/CVE vulnerability concerns.
• lerobot: Avoids forcing heavy PyTorch version constraints and dependencies.

Missing Dependency Test

import sys, importlib.util

# 1. Simulate missing wandb & lerobot
sys.modules["wandb"] = None
sys.modules["wandb.util"] = None
sys.modules["lerobot"] = None
sys.modules["lerobot.datasets"] = None

from cosmos_framework.utils import wandb_util
from cosmos_framework.utils.callback import WandBCallback
from cosmos_framework.callbacks.device_monitor import DeviceMonitor
from cosmos_framework.callbacks.grad_clip import GradClip
from cosmos_framework.callbacks.iter_speed import IterSpeed
from cosmos_framework.callbacks.mfu import MFUCallback
from cosmos_framework.callbacks.norm_monitor import NormMonitor
from cosmos_framework.callbacks.ofu import OFUCallback
from cosmos_framework.callbacks.sequence_packing_padding import SequencePackingPadding
from cosmos_framework.callbacks.sigma_loss_analysis import SigmaLossAnalysis

# wandb disabled mode test without wandb installed (returns cleanly)
wandb_util.init_wandb(type("Cfg", (), {"job": type("J", (), {"wandb_mode": "disabled"})()})(), model=None)

# 2. lerobot dataset guard test (lerobot is None; raises controlled ImportError on init)
spec = importlib.util.spec_from_file_location("cosmos3_action_lerobot", "cosmos_framework/data/generator/action/datasets/cosmos3_action_lerobot.py")
mod = importlib.util.module_from_spec(spec)
spec.loader.exec_module(mod)

assert mod.lerobot is None
try:
    mod.BaseActionLeRobotDataset(
        fps=10, chunk_length=1, split_seed=0, split_val_ratio=0.1, split="train", mode="train", embodiment_type="droid_lerobot", viewpoint="ego_view"
    )
except ImportError as e:
    print(f"Controlled ImportError on instantiation: {e}")