Use MaybeUninit in DecInt #4467

Job	Run time
Rustfmt	8s
Check --no-default-features (nightly)	18s
Check nightly-only targets (nightly)	28s
Check (stable)	1m 25s
Check (nightly)	1m 32s
Check selected Tier 3 platforms (nightly)	5m 1s
Check (1.63)	1m 42s
Test use-libc (ubuntu)	16s
Test (ubuntu)	45s
Test use-libc (i686-linux)	24s
Test (ubuntu-20.04)	45s
Test use-libc (aarch64-linux)	30s
Test use-libc (powerpc64le-linux)	28s
Test (i686-linux)	1m 7s
Test use-libc (riscv64-linux)	25s
Test (aarch64-linux)	1m 9s
Test use-libc (s390x-linux)	23s
Test (powerpc64le-linux)	1m 7s
Test rustix_use_experimental_asm (powerpc64le-linux)	42s
Test use-libc (arm-linux)	32s
Test (riscv64-linux)	1m 31s
Test rustix_use_experimental_asm (s390x-linux)	53s
Test (s390x-linux)	1m 37s
Test (arm-linux)	1m 10s
Test (ubuntu-stable)	53s
Test (i686-linux-stable)	1m 5s
Test (aarch64-linux-stable)	1m 30s
Test (riscv64-linux-stable)	1m 2s
Test (s390x-linux-stable)	56s
Test (powerpc64le-linux-stable)	59s
Test (arm-linux-stable)	58s
Test (ubuntu-1.63)	2m 38s
Test (i686-linux-1.63)	3m 2s
Test (aarch64-linux-1.63)	2m 59s
Test (riscv64-linux-1.63)	3m 2s
Test (s390x-linux-1.63)	2m 54s
Test (powerpc64le-linux-1.63)	3m 13s
Test (arm-linux-1.63)	3m 5s
Test (macos-latest)	30s
Test (macos-13)	1m 10s
Test (windows)	45s
Test (windows-2019)	56s
Test (musl)	41s
	56m 36s

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