Use MaybeUninit in DecInt #4444

Job	Run time
Rustfmt	4s
Check selected Tier 3 platforms (nightly)	4m 49s
Check nightly-only targets (nightly)	21s
Check --no-default-features (nightly)	54s
Check (stable)	5m 42s
Check (nightly)	5m 51s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 10s
Test use-libc (ubuntu)	35s
Check (1.63)	5m 58s
Test rustix_use_experimental_asm (s390x-linux)	1m 11s
Test (ubuntu)	44s
Test use-libc (i686-linux)	58s
Test (ubuntu-20.04)	43s
Test use-libc (aarch64-linux)	1m 9s
Test (i686-linux)	1m 2s
Test use-libc (powerpc64le-linux)	1m 2s
Test (aarch64-linux)	1m 6s
Test use-libc (riscv64-linux)	52s
Test (powerpc64le-linux)	1m 10s
Test use-libc (s390x-linux)	59s
Test (riscv64-linux)	59s
Test use-libc (arm-linux)	1m 1s
Test (s390x-linux)	1m 0s
Test (arm-linux)	1m 14s
Test (ubuntu-stable)	44s
Test (i686-linux-stable)	58s
Test (aarch64-linux-stable)	58s
Test (riscv64-linux-stable)	50s
Test (s390x-linux-stable)	1m 4s
Test (powerpc64le-linux-stable)	1m 0s
Test (arm-linux-stable)	58s
Test (ubuntu-1.63)	2m 24s
Test (i686-linux-1.63)	2m 53s
Test (aarch64-linux-1.63)	2m 44s
Test (riscv64-linux-1.63)	2m 51s
Test (s390x-linux-1.63)	2m 38s
Test (powerpc64le-linux-1.63)	2m 54s
Test (arm-linux-1.63)	2m 38s
Test (macos-latest)	30s
Test (macos-13)	59s
Test (windows)	48s
Test (windows-2019)	1m 2s
Test (musl)	41s
	1h 10m 8s

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