blobby: use `base16ct` instead of `hex` #650

Job	Run time
build (1.60.0, armv7a-none-eabi)	1m 31s
cross (aarch64-unknown-linux-gnu, 1.60.0)	1m 52s
build (1.60.0, thumbv7em-none-eabi)	1m 25s
cross (aarch64-unknown-linux-gnu, stable)	34s
test (i686-unknown-linux-gnu, ubuntu-latest, 1.60.0, sudo apt update && sudo apt install gcc-mult...	1m 47s
build (1.60.0, wasm32-unknown-unknown)	1m 28s
cross (powerpc-unknown-linux-gnu, 1.60.0)	1m 55s
test (i686-unknown-linux-gnu, ubuntu-latest, stable, sudo apt update && sudo apt install gcc-mult...	21s
build (stable, armv7a-none-eabi)	16s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.60.0)	1m 27s
build (stable, thumbv7em-none-eabi)	7s
cross (powerpc-unknown-linux-gnu, stable)	32s
build (stable, wasm32-unknown-unknown)	21s
test (x86_64-unknown-linux-gnu, ubuntu-latest, stable)	11s
test (x86_64-apple-darwin, macos-latest, 1.60.0)	2m 39s
test (x86_64-apple-darwin, macos-latest, stable)	21s
test (x86_64-pc-windows-msvc, windows-latest, 1.60.0)	32s
test (x86_64-pc-windows-msvc, windows-latest, stable)	40s
x86 (x86_64-unknown-linux-gnu, 1.72.0)	19s
x86 (x86_64-unknown-linux-gnu, stable)	17s
minimal-versions / minimal-versions	54s
	19m 29s

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