Add MPEG Gaussian Splats extension

[haudiobe]

Gaussian Splats (GS) provide an efficient representation for static and dynamic 3D scenes by compactly encoding local geometry and view-dependent appearance. To address interoperability, backward compatibility, and progressive rendering in various applications, integrating GS into the glTF (GL Transmission Format) standard is essential.

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✅ ibouazizi
❌ haudiobe
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