feat(renderer): add shadow mapping with PCF soft shadows

Introduce shadow mapping using a dedicated depth framebuffer and shader. The block fragment shader now performs percentage-closer filtering (PCF) with Poisson disk sampling and random rotation for soft shadows. The vertex shader outputs light-space coordinates. A new depth shader pair handles rendering from the light's perspective, discarding transparent fragments. The renderer sets up the light projection based on the camera position and sun direction, and applies the shadow factor to diffuse lighting. Day/night cycle can now be toggled off in the world server thread.

assets/shaders/block_v_shader.glsl

@@ -8,6 +8,7 @@ out vec2 tc;
 out vec3 normal;
 out vec3 vert_pos;
 flat out int tex_layer;
+out vec4 FragPosLightSpace;
 
 mat4 buildRotateX(float rad);
 mat4 buildRotateY(float rad);
@@ -17,19 +18,19 @@ mat4 buildTranslate(float x, float y, float z);
 uniform mat4 mv_matrix;
 uniform mat4 proj_matrix;
 uniform mat4 norm_matrix;
-
+uniform mat4 lightSpaceMatrix;
 
 void main(void) {
     vec4 viewPos = mv_matrix * vec4(pos, 1.0);
 
-    vert_pos = viewPos.xyz;
+    vert_pos = pos;
 
     tc = texCoord;
     
     tex_layer = int(layer);
     
     normal = mat3(norm_matrix) * aNormal;
-    
+    FragPosLightSpace = lightSpaceMatrix * vec4(pos, 1.0);
     gl_Position = proj_matrix * viewPos;
 }