Add OpenCV contrib module support with ximgproc.thinning TypeScript definitions

[Copilot]

This PR adds comprehensive support for OpenCV contrib modules, specifically addressing the missing cv.ximgproc.thinning() function that users need for image skeletonization.

What's Added

TypeScript Definitions

• Complete TypeScript definitions for the ximgproc module including:
  • cv.ximgproc.thinning(src, dst, thinningType) function with proper parameter types
  • cv.ximgproc.THINNING_ZHANGSUEN and cv.ximgproc.THINNING_GUOHALL constants
  • Full JSDoc documentation with usage examples

Build Infrastructure

• Updated GitHub Actions workflow to build OpenCV.js with opencv_contrib modules
• Added scripts/build-contrib.sh for local contrib builds
• Added npm run build:contrib command for easy building

Developer Tools

• src/contrib-utils.ts with functions to detect contrib module availability
• Comprehensive example in examples/ximgproc-thinning.ts
• Test suite that gracefully handles missing contrib modules

Usage Example

With this PR, developers now get full TypeScript support for contrib modules:

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

cv.onRuntimeInitialized = () => {
  const src = cv.imread('input');
  const dst = new cv.Mat();
  
  // Full TypeScript autocomplete and type checking
  cv.ximgproc.thinning(src, dst, cv.ximgproc.THINNING_ZHANGSUEN);
  
  dst.delete();
  src.delete();
};

Building with Contrib Modules

To use the contrib functions, users need to build OpenCV.js with contrib modules:

# Using the provided script
npm run build:contrib

# Or manually
./scripts/build-contrib.sh

The build script automatically:

1. Clones OpenCV and opencv_contrib repositories
2. Sets up Emscripten
3. Builds OpenCV.js with -DOPENCV_EXTRA_MODULES_PATH and -DBUILD_opencv_ximgproc=ON

Documentation

Added comprehensive documentation in README.md explaining:

• How to build OpenCV.js with contrib modules
• Usage examples for cv.ximgproc.thinning()
• Clear instructions for replacing the default opencv.js build

The TypeScript definitions provide immediate developer value with autocomplete and type safety, while the build infrastructure ensures users can easily create contrib-enabled builds when needed.

Fixes #84.

Warning

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