Poly haven optimizations

[kwokcb]

This pull request introduces several improvements to the PolyHaven MaterialX packaging workflow, focusing on performance, flexibility, and user experience. The most significant changes include switching ZIP compression from JSZip to fflate for faster and more efficient packaging, adding support for configurable texture formats, and enhancing the UI and loading behavior for the materials grid. Additionally, there are updates to documentation and minor code cleanups.

MaterialX Packaging and Compression:

• Replaced JSZip with fflate for ZIP compression in jsPolyHavenLoader.js, resulting in faster package creation and reduced resource usage. All ZIP file creation and file addition logic now use fflate's API and Uint8Array blobs. [1] [2]
• Improved concurrency for texture downloads when creating a MaterialX package, allowing parallel downloads and more robust error handling.

Texture Format Flexibility:

• Added support for specifying desired texture format (e.g., PNG, JPG, EXR) via URL query string or UI selector. This includes preprocessing MaterialX content and texture file references to remap extensions and paths, ensuring compatibility with the selected format. [1] [2] [3] [4]

UI and Loading Experience:

• Materials grid is now disabled until the viewer iframe signals readiness, preventing premature interaction and improving user experience. CSS for the disabled state is injected dynamically, and event listeners manage the transition. [1] [2]
• Improved scrolling behavior for the materials grid by setting a fixed height and enabling vertical overflow in index.html.

These changes collectively enhance the performance, flexibility, and usability of the PolyHaven MaterialX workflow.