Use MaybeUninit in DecInt #4453

Job	Run time
Check --no-default-features (nightly)	56s
Check selected Tier 3 platforms (nightly)	4m 51s
Check (stable)	6m 8s
Check nightly-only targets (nightly)	24s
Check (nightly)	6m 15s
Rustfmt	11s
Check (1.63)	10m 9s
Test (ubuntu)	41s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 2s
Test (ubuntu-20.04)	42s
Test use-libc (ubuntu)	35s
Test rustix_use_experimental_asm (s390x-linux)	1m 12s
Test (i686-linux)	59s
Test use-libc (i686-linux)	1m 8s
Test (aarch64-linux)	56s
Test use-libc (aarch64-linux)	55s
Test (powerpc64le-linux)	1m 10s
Test use-libc (powerpc64le-linux)	56s
Test (riscv64-linux)	1m 4s
Test use-libc (riscv64-linux)	1m 12s
Test (s390x-linux)	1m 8s
Test use-libc (s390x-linux)	53s
Test (arm-linux)	1m 3s
Test use-libc (arm-linux)	57s
Test (ubuntu-stable)	44s
Test (i686-linux-stable)	1m 7s
Test (aarch64-linux-stable)	1m 27s
Test (riscv64-linux-stable)	55s
Test (s390x-linux-stable)	52s
Test (powerpc64le-linux-stable)	1m 40s
Test (arm-linux-stable)	57s
Test (ubuntu-1.63)	2m 25s
Test (i686-linux-1.63)	2m 39s
Test (aarch64-linux-1.63)	2m 58s
Test (riscv64-linux-1.63)	2m 47s
Test (s390x-linux-1.63)	2m 44s
Test (powerpc64le-linux-1.63)	2m 50s
Test (arm-linux-1.63)	2m 56s
Test (macos-latest)	34s
Test (macos-13)	59s
Test (windows)	43s
Test (windows-2019)	46s
Test (musl)	39s
	1h 16m 9s

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