Adds screen to world space conversion

Adds functionality to convert screen coordinates to world space, including handling for cases where the inverse view projection matrix is singular or when the world position is out of screen bounds.

Also exposes Camera class to unit tests.

CMakeLists.txt

@@ -100,6 +100,7 @@ target_compile_features(${PROJECT_NAME} PUBLIC cxx_std_23)
 if (OMATH_BUILD_TESTS)
     add_subdirectory(extlibs)
     add_subdirectory(tests)
+    target_compile_definitions(${PROJECT_NAME} PUBLIC OMATH_BUILD_TESTS)
 endif ()
 
 if (OMATH_BUILD_EXAMPLES)