🧹 [code health] Remove unused numpy import in surface.py

[sharesth23]

🎯 What: Removed the unused import numpy as np from volsurface/core/surface.py.
💡 Why: Removing an unused module import is completely safe, reduces dependencies, and improves codebase readability.
✅ Verification: Verified by checking the file source code to ensure np is not used anywhere else in the file, and then ran the full test suite (pytest volsurface/tests/) to ensure no functionality is broken.
✨ Result: Cleaned up unused import, leading to a leaner and more maintainable file without changing behavior.

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PR created automatically by Jules for task 16389205786925833718 started by @sharesth23

[google-labs-jules]

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[sharesth23]

Removing unused import of numpy in surfce.py file .

[google-labs-jules]

Removing unused import of numpy in surfce.py file .

Acknowledged.