download_checkpoints allow --fps 4 for action-conditioned checkpoint

[LucasFenaux]

Problem: To download the Cosmos-Predict2-2B-Sample-Action-Conditioned model using the scripts/download_checkpoints.py script as instructed in the setup one needs to set --fps 4, as shown in lines 167-171 of scripts/download_checkpoints.py

    if "sample_action_conditioned" in args.model_types:
        if "2B" in args.model_sizes and "480" in args.resolution and "4" in args.fps:
            download("nvidia/Cosmos-Predict2-2B-Sample-Action-Conditioned")
        else:
            print("Sample Action Conditioned model is only available for 2B model size, 480P and 4FPS. Skipping...")

However, the parser only accepts 10 or 16 as options, as seen in line 96:

        choices=["10", "16"],

Fix:
Add 4 to the list of choices in the parser argument.