Rust

xtask: fix nixfmt + update Nix flake + fix CI #6516

Job	Run time
Integration Test (IA-32)	1m 35s
Integration Test (x86_64)	1m 34s
Integration Test (x86_64 Windows)	3m 41s
Integration Test (AArch64)	1m 13s
Build (feature permutations)	4m 9s
Build (stable MSRV)	46s
Test Coverage	46s
Nightly (build, test, doc)	3m 10s
Unit + Doc Tests	45s
Build (uefi-raw MSRV)	35s
Build Standard Binary (nightly)	29s
Unit + Doc Tests (Miri)	1m 14s
	19m 57s

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