Rename blit common shader module

kitty/shaders/blit-common.slang

@@ -3,7 +3,7 @@
 // Distributed under terms of the GPLv3 license.
 
 // Maps a vertex id to src and destination co-ordinates
-module blit;
+module blit_common;
 
 public struct BlitOutput {
     public float2 texcoord;

kitty/shaders/graphics.slang

@@ -2,7 +2,7 @@
 // Copyright (C) 2026 Kovid Goyal <kovid at kovidgoyal.net>
 // Distributed under terms of the GPLv3 license.
 
-import blit;
+import blit_common;
 import alpha_blend;
 import utils;