refactor: split frag0 into multiple files

default/inc_rand.glsl

@@ -0,0 +1,14 @@
+#ifndef INC_RAND
+#define INC_RAND
+
+float rand(float seed){
+    float v=pow(abs(seed),6./7.);
+    v*=sin(v)+1.;
+    return fract(v);
+}
+
+float rand(vec2 n){
+    return rand(n.x * 1234 + n.y * 9876);
+}
+
+#endif