remove np deps

[kaiyuan-li]

we don't need numpy as an extra dependency for just getting the prod of shape. Replaced with math.prod. Current test_utils.py covers the change.

[Copilot]

Pull Request Overview

This PR removes the numpy dependency from the utils module by replacing np.prod with Python's built-in math.prod for calculating tensor shape products. This reduces external dependencies while maintaining the same functionality.

Key Changes

• Added math module import
• Removed numpy import and dependency
• Replaced np.prod calls with math.prod in tensor size calculations

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