switch to c++ 20

Signed-off-by: Jade Turner <spacey-sooty@proton.me>

Author: spacey-sooty

CMakeLists.txt

@@ -5,7 +5,7 @@ project(mrcal_jni LANGUAGES C CXX VERSION 1.0.0)
 option(BUILD_SHARED_LIBS "Build shared libraries" ON)
 
 # C++
-set(CMAKE_CXX_STANDARD 23)
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)