Use `rustix` instead of `nix` #1041

Job	Run time
format	24s
clippy-check	3m 55s
cargo-deny	24s
Documentation on Github Pages	54s
check-minimal	40s
coverage-main	2m 23s
coverage-tests	4m 0s
msrv	4m 17s
coverage-tests (server_system)	3m 30s
coverage-tests (client_system)	3m 40s
coverage-tests (client_system, server_system)	3m 43s
	27m 50s

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