[examples] updated DARPA SUBOFF link

[marcvivesmassana]

Note

Low Risk
Single-string URL change in an example file; risk is limited to potential breakage if the new S3 object path is incorrect.

Overview
Updates the DARPA_SUBOFF example geometry download link from DARPA.STEP to DARPA_SUBOFF.STEP on S3, ensuring the example pulls the intended model.

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