Added texture packer for automatically creating texture atlas on build.

private/texture_packer/SModule

@@ -0,0 +1,40 @@
+
+import os
+
+Import('env')
+
+def _exe_name() -> str:
+    if os.name == 'nt':
+        return env['BIN_DIR'] + '/texture_packer.exe'
+    return env['BIN_DIR'] + '/texture_packer'
+
+src_files = Split("""
+    main.cpp
+    
+    packer.cpp
+""")
+
+prog_packer = env.UnityProgram(
+    target = env['BIN_DIR'] + '/texture_packer',
+    source = src_files,
+    dependencies = {
+        'argparse': {},
+        'mijin': {},
+        'rectpack2D': {},
+        'spdlog': {},
+        'stb': {}
+    }
+)
+env.Default(prog_packer)
+
+def _pack_textures(env, target: str, source: 'list[str]'):
+    cmd = env.Command(
+        target = target,
+        source = source,
+        action = f'{_exe_name()} $TARGET $SOURCES'
+    )
+    # env.Depends(cmd, prog_packer)
+    return cmd
+env.AddMethod(_pack_textures, 'PackTextures')
+
+Return('env')