feat(tests): conditionally include ImGui test engine functionality

- Added conditional compilation for ImGui test engine features in `test_utils.cc` and `test_utils.h`, enabling the loading of ROMs and opening of editors only when the YAZE_ENABLE_IMGUI_TEST_ENGINE flag is set.
- Improved modularity by managing includes based on feature flags, enhancing the flexibility of the testing framework.

Benefits:
- Streamlined testing process for ImGui-related functionalities.
- Enhanced code organization by isolating ImGui test engine dependencies.

test/test_utils.h

@@ -15,9 +15,12 @@
 #include <gmock/gmock.h>
 
 #include "absl/strings/str_format.h"
-#include "imgui_test_engine/imgui_te_context.h"
 #include "app/rom.h"
 
+#ifdef YAZE_ENABLE_IMGUI_TEST_ENGINE
+#include "imgui_test_engine/imgui_te_context.h"
+#endif
+
 namespace yaze {
 namespace test {
 
@@ -193,8 +196,10 @@ class RomDependentTest : public ::testing::Test {
 
 namespace gui {
 
+#ifdef YAZE_ENABLE_IMGUI_TEST_ENGINE
 void LoadRomInTest(ImGuiTestContext* ctx, const std::string& rom_path);
 void OpenEditorInTest(ImGuiTestContext* ctx, const std::string& editor_name);
+#endif
 
 } // namespace gui