[HOTFIX] examples: changed file name

[marcvivesmassana]

Note

Low Risk
Single-line import fix to align with a filename change; risk is limited to potential breakage if downstream code still expects the old module path.

Overview
Updates flow360/examples/__init__.py to import DARPA_SUBOFF from DARPA_SUBOFF.py instead of the old DARPA.py module name, keeping the DARPA_SUBOFF example available via the package-level exports.

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