refactor: split examples common into header and source (#1393)

examples/cli/CMakeLists.txt

@@ -1,6 +1,7 @@
 set(TARGET sd-cli)
 
 add_executable(${TARGET}
+    ../common/common.cpp
     ../common/log.cpp
     ../common/media_io.cpp
     image_metadata.cpp

examples/cli/main.cpp

@@ -15,11 +15,13 @@
 // #include "preprocessing.hpp"
 #include "stable-diffusion.h"
 
-#include "common/common.hpp"
+#include "common/common.h"
 #include "common/media_io.h"
 #include "common/resource_owners.hpp"
 #include "image_metadata.h"
 
+namespace fs = std::filesystem;
+
 const char* previews_str[] = {
     "none",
     "proj",