Use MaybeUninit in DecInt #4462

Job	Run time
Check --no-default-features (nightly)	56s
Check nightly-only targets (nightly)	23s
Check (stable)	5m 52s
Rustfmt	13s
Check (nightly)	6m 10s
Check selected Tier 3 platforms (nightly)	3m 45s
Check (1.63)	10m 13s
Test (ubuntu)	45s
Test (ubuntu-20.04)	45s
Test (i686-linux)	1m 21s
Test use-libc (ubuntu)	50s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 9s
Test (aarch64-linux)	1m 8s
Test use-libc (i686-linux)	1m 8s
Test (powerpc64le-linux)	1m 3s
Test use-libc (aarch64-linux)	1m 1s
Test (riscv64-linux)	58s
Test use-libc (powerpc64le-linux)	1m 6s
Test (s390x-linux)	1m 15s
Test use-libc (riscv64-linux)	1m 16s
Test use-libc (s390x-linux)	57s
Test (arm-linux)	1m 8s
Test rustix_use_experimental_asm (s390x-linux)	1m 11s
Test use-libc (arm-linux)	1m 20s
Test (ubuntu-stable)	40s
Test (i686-linux-stable)	1m 29s
Test (aarch64-linux-stable)	53s
Test (riscv64-linux-stable)	1m 0s
Test (s390x-linux-stable)	1m 27s
Test (powerpc64le-linux-stable)	1m 15s
Test (arm-linux-stable)	1m 24s
Test (ubuntu-1.63)	2m 27s
Test (i686-linux-1.63)	2m 49s
Test (aarch64-linux-1.63)	3m 0s
Test (riscv64-linux-1.63)	2m 44s
Test (s390x-linux-1.63)	2m 58s
Test (powerpc64le-linux-1.63)	2m 57s
Test (arm-linux-1.63)	2m 46s
Test (macos-latest)	45s
Test (macos-13)	45s
Test (windows)	46s
Test (windows-2019)	54s
Test (musl)	46s
	1h 17m 38s

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