Fix Next.js 14.1.0 compatibility by improving UMD pattern in opencv.js

[Copilot]

This PR fixes the compatibility issue with Next.js 14.1.0 where opencv.js would throw a TypeError: Cannot set properties of undefined (setting 'cv') error during module loading.

Problem

The error occurred when Next.js 14.1.0 created an environment where:

1. module.exports could be null or undefined in certain contexts
2. The this context passed to the UMD wrapper was undefined
3. The original UMD pattern's condition typeof module === 'object' && module.exports would fail when module.exports was falsy
4. This caused the code to fall through to the else clause and attempt root.cv = factory() where root was undefined

Solution

Improved CommonJS Detection:

// Before: typeof module === 'object' && module.exports
// After:  typeof module === 'object' && module !== null

Added Safe Root Fallback:

// Ensure root exists before setting properties
root = root || (typeof globalThis !== 'undefined' ? globalThis : 
               typeof global !== 'undefined' ? global : 
               typeof self !== 'undefined' ? self : {});

Better UMD Invocation:

// Use safer global object detection when calling the UMD function
}(typeof globalThis !== 'undefined' ? globalThis : 
  typeof global !== 'undefined' ? global :
  typeof self !== 'undefined' ? self :
  typeof window !== 'undefined' ? window : this, function () {

Testing

• ✅ All existing tests continue to pass
• ✅ Added comprehensive test suite for Next.js compatibility scenarios
• ✅ Verified the fix handles various edge cases (null exports, undefined context, etc.)
• ✅ Maintains full backward compatibility with all supported environments

Usage

Users can now successfully use opencv.js in Next.js 14.1.0 projects without needing to downgrade:

import cv from '@techstark/opencv-js';

cv.onRuntimeInitialized = () => {
  console.log('OpenCV.js is ready!');
  // OpenCV functions work normally
};

Fixes #54.

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