feat: add nlohmann/json lib

cmake/FindJSON.cmake

@@ -0,0 +1,21 @@
+include(FetchContent)
+
+message(STATUS "Fetching json...")
+
+FetchContent_Declare(
+	json
+	GIT_REPOSITORY https://github.com/nlohmann/json
+	GIT_TAG v3.11.3
+)
+
+FetchContent_GetProperties(json)
+if(NOT json_POPULATED)
+	set(JSON_BuildTests OFF CACHE INTERNAL "")
+	FetchContent_Populate(json)
+	add_subdirectory(${json_SOURCE_DIR} ${json_BINARY_DIR} EXCLUDE_FROM_ALL)
+endif()
+
+FetchContent_MakeAvailable(json)
+
+message(STATUS "json fetched and is now ready.")
+set(JSON_FOUND TRUE)