Restyle refactor: Use `structs` for extended public/secret keys. #5378

Job	Run time
docker-esp32	2m 0s
docker-clusterfuzz	1m 15s
docker-bootstrap-node	1m 23s
docker-fuzzer	21s
docker-toxcore-js	2m 5s
docker-win64	15s
docker-win32	28s
docker-bootstrap-node-websocket	14s
	8m 1s

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