Use MaybeUninit in DecInt #4469

Job	Run time
Check --no-default-features (nightly)	57s
Check nightly-only targets (nightly)	27s
Check selected Tier 3 platforms (nightly)	4m 56s
Check (stable)	6m 24s
Rustfmt	8s
Check (nightly)	6m 20s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 13s
Check (1.63)	10m 30s
Test (ubuntu)	43s
Test (ubuntu-20.04)	42s
Test use-libc (ubuntu)	36s
Test (i686-linux)	1m 5s
Test rustix_use_experimental_asm (s390x-linux)	1m 14s
Test use-libc (i686-linux)	51s
Test (aarch64-linux)	1m 7s
Test use-libc (aarch64-linux)	2m 10s
Test (powerpc64le-linux)	59s
Test use-libc (powerpc64le-linux)	55s
Test (riscv64-linux)	1m 30s
Test use-libc (riscv64-linux)	50s
Test (s390x-linux)	1m 3s
Test use-libc (s390x-linux)	1m 22s
Test use-libc (arm-linux)	53s
Test (arm-linux)	1m 5s
Test (ubuntu-stable)	36s
Test (i686-linux-stable)	1m 3s
Test (aarch64-linux-stable)	1m 54s
Test (riscv64-linux-stable)	58s
Test (s390x-linux-stable)	1m 5s
Test (powerpc64le-linux-stable)	1m 10s
Test (arm-linux-stable)	1m 6s
Test (ubuntu-1.63)	2m 39s
Test (i686-linux-1.63)	2m 57s
Test (aarch64-linux-1.63)	3m 8s
Test (riscv64-linux-1.63)	2m 48s
Test (s390x-linux-1.63)	2m 51s
Test (powerpc64le-linux-1.63)	2m 55s
Test (arm-linux-1.63)	2m 58s
Test (macos-latest)	31s
Test (macos-13)	1m 5s
Test (windows)	51s
Test (windows-2019)	53s
Test (musl)	45s
	1h 20m 13s

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