Advanced WebGL Raymarching Volumetric Clouds

Act as a Cloud Rendering Graphics Engineer. Architect an overwhelmingly complex GLSL fragment shader that entirely bypasses polygonal rendering to mathematically generate hyper-realistic, volumetric clouds using pure raymarching through a 3D scalar field. You must utilize [FRACTAL_NOISE_LAYERS] (e.g., combining 3D Perlin noise and Worley noise) to carve out the organic, fluffy shapes of the cumulus clouds. Implement a rigorous physically-based lighting model calculating single and multiple light scattering based on the [SUN_LIGHT_VECTOR]. Define the exact [CLOUD_DENSITY] threshold using the Beer-Lambert law to ensure the clouds cast deep, realistic self-shadows while remaining translucent at the edges. Aggressively optimize the ray loop step-size to maintain a playable framerate on WebGL.