perf: reduce terrain shadow samples

vendor/clouds3d.js

@@ -852,11 +852,11 @@ var CLOUD_SAMPLER_GLSL = [
     // march stops once the ray is above the tallest terrain.
     'float terrainShadow(vec3 p, vec3 L) {',
         'if (uTerrainShadowOn < 0.5 || L.y < 0.01) return 1.0;',
-        'float stepT = 0.22;',
+        'float stepT = 0.30;',
         'float clearance = 1000.0;',
         'float y = p.y;',
         'float top = p.y + 1.4;',
-        'for (int i = 0; i < 11; i++) {',
+        'for (int i = 0; i < 8; i++) {',
             'vec2 q = p.xz + L.xz * (stepT * (float(i) + 0.5));',
             'float h = terrElevT(q) * uElevScale;',
             'y += L.y * stepT;',