Use MaybeUninit in DecInt #4441

Job	Run time
Rustfmt	7s
Check nightly-only targets (nightly)	24s
Check (stable)	6m 5s
Check --no-default-features (nightly)	54s
Check (nightly)	5m 51s
Check (1.63)	6m 7s
Test (ubuntu)	43s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 2s
Test use-libc (ubuntu)	36s
Test (ubuntu-20.04)	44s
Test rustix_use_experimental_asm (s390x-linux)	1m 4s
Test use-libc (i686-linux)	1m 5s
Check selected Tier 3 platforms (nightly)	4m 46s
Test use-libc (aarch64-linux)	57s
Test (i686-linux)	1m 4s
Test use-libc (powerpc64le-linux)	58s
Test (aarch64-linux)	1m 3s
Test use-libc (riscv64-linux)	57s
Test (powerpc64le-linux)	58s
Test use-libc (s390x-linux)	58s
Test (riscv64-linux)	1m 0s
Test use-libc (arm-linux)	1m 13s
Test (s390x-linux)	1m 5s
Test (arm-linux)	1m 6s
Test (ubuntu-stable)	37s
Test (i686-linux-stable)	53s
Test (aarch64-linux-stable)	57s
Test (riscv64-linux-stable)	57s
Test (s390x-linux-stable)	51s
Test (powerpc64le-linux-stable)	51s
Test (arm-linux-stable)	1m 3s
Test (ubuntu-1.63)	2m 22s
Test (i686-linux-1.63)	2m 38s
Test (aarch64-linux-1.63)	2m 43s
Test (riscv64-linux-1.63)	2m 36s
Test (s390x-linux-1.63)	2m 37s
Test (powerpc64le-linux-1.63)	2m 40s
Test (arm-linux-1.63)	2m 50s
Test (macos-latest)	29s
Test (macos-13)	47s
Test (windows)	46s
Test (windows-2019)	56s
Test (musl)	38s
	1h 8m 58s

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