cleanup, fix clang-tidy warnings

include/opendht/callbacks.h

include/opendht/crypto.h

include/opendht/default_types.h

include/opendht/dht.h

include/opendht/dhtrunner.h

include/opendht/network_engine.h

include/opendht/securedht.h

include/opendht/value.h

src/callbacks.cpp

src/crypto.cpp

src/default_types.cpp

src/dht.cpp

src/dhtrunner.cpp

src/network_engine.cpp

src/node.cpp

src/op_cache.cpp

src/op_cache.h

src/search.h

src/securedht.cpp

src/value.cpp