fix: remove unused integrate() function from Utils.js

[TechGenius-Karan]

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🔍 Description

What was wrong

Utils.js contained a fully implemented integrate() function (Velocity Verlet integration) that was exported but
never imported or used anywhere in the codebase.

Having unused exported code causes two problems:

1. Confusion — a developer reading the file might assume this is the intended integration method and start using it,
   not realising that PhysicsBody.step() already handles integration internally. Two competing approaches sitting side
   by side is unclear.
2. Dead weight — code that is never called still has to be read, understood, and maintained for no benefit.

Note: collideBoundary() in the same file was also flagged as dead code in the original audit, but it has since been
adopted and is now actively used by BouncingBall.jsx — so only integrate() remained unused.

What was fixed

Removed the integrate() function entirely from Utils.js. No other file imported it, so there are zero callsite
changes needed.

Closes #BUG-015 (if applicable)

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✅ Checklist

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• Updated documentation, comments, or in-code explanations where needed
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• Followed the CONTRIBUTING.md guidelines

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🎨 Visual Changes (if UI-related)

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(OBLIGATORY)

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📂 Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📝 Documentation update
• ♻️ Refactor / code quality improvement
• 🎨 UI/UX enhancement
• 🔒 Security improvement

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🧩 Additional Notes for Reviewers

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🎉 This PR is included in version 3.28.0 🎉

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