Use MaybeUninit in DecInt #4468

Job	Run time
Check --no-default-features (nightly)	57s
Check (stable)	6m 12s
Check (nightly)	6m 18s
Check selected Tier 3 platforms (nightly)	4m 51s
Check nightly-only targets (nightly)	24s
Check (1.63)	11m 7s
Rustfmt	6s
Test use-libc (ubuntu)	37s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 8s
Test use-libc (i686-linux)	1m 29s
Test (ubuntu)	46s
Test rustix_use_experimental_asm (s390x-linux)	1m 1s
Test use-libc (aarch64-linux)	56s
Test (ubuntu-20.04)	43s
Test use-libc (powerpc64le-linux)	55s
Test (i686-linux)	59s
Test (aarch64-linux)	1m 41s
Test (powerpc64le-linux)	1m 13s
Test use-libc (riscv64-linux)	52s
Test (riscv64-linux)	1m 1s
Test use-libc (s390x-linux)	1m 4s
Test (s390x-linux)	1m 11s
Test use-libc (arm-linux)	1m 32s
Test (arm-linux)	1m 3s
Test (ubuntu-stable)	35s
Test (i686-linux-stable)	53s
Test (aarch64-linux-stable)	58s
Test (riscv64-linux-stable)	1m 6s
Test (s390x-linux-stable)	1m 1s
Test (powerpc64le-linux-stable)	50s
Test (arm-linux-stable)	1m 32s
Test (ubuntu-1.63)	2m 33s
Test (i686-linux-1.63)	2m 49s
Test (aarch64-linux-1.63)	8m 5s
Test (riscv64-linux-1.63)	3m 51s
Test (s390x-linux-1.63)	2m 55s
Test (powerpc64le-linux-1.63)	3m 10s
Test (arm-linux-1.63)	3m 5s
Test (macos-latest)	32s
Test (macos-13)	53s
Test (windows)	44s
Test (windows-2019)	44s
Test (musl)	46s
	1h 25m 8s

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