Get rid of 'using json = nlohmann::json'

examples/crypto_bot.cpp

include/mtx/events.hpp

include/mtx/events/collections.hpp

include/mtx/events_impl.hpp

include/mtx/requests.hpp

include/mtxclient/http/client_impl.hpp

lib/crypto/utils.cpp

lib/http/client.cpp

lib/structs/events/collections.cpp

lib/structs/events/encrypted.cpp

lib/structs/events/mscs/image_packs.cpp

tests/client_api.cpp