Bump to edition 2021 (#307) #923

Job	Run time
Check code formatting	5s
Build (libsignal-service-actix, Rust stable)	1m 37s
Build (libsignal-service-actix, Rust beta)	1m 50s
Clippy (libsignal-service-actix)	1m 16s
Clippy (libsignal-service-hyper)	1m 8s
Build (libsignal-service-actix, Rust nightly)	4m 35s
Clippy (libsignal-service-hyper, unsend-futures)	1m 35s
Build (libsignal-service-hyper, Rust stable)	1m 36s
Clippy (libsignal-service)	1m 4s
Clippy (libsignal-service, unsend-futures)	1m 20s
Build (libsignal-service-hyper, Rust stable)	1m 44s
Build (libsignal-service-hyper, Rust beta)	1m 27s
Build (libsignal-service-hyper, Rust nightly)	3m 42s
Build (libsignal-service, Rust stable)	1m 8s
Build (libsignal-service, Rust stable)	1m 31s
Build (libsignal-service, Rust beta)	1m 17s
Build (libsignal-service, Rust nightly)	3m 17s
Build (libsignal-service-actix, Rust 1.75)	1m 58s
	32m 10s

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