Add hex-encoding examples based on `base16ct` #46

Job	Run time
cross (1.72.0, aarch64-unknown-linux-gnu, default)	50s
cross (1.72.0, powerpc-unknown-linux-gnu, default)	42s
cross (stable, aarch64-unknown-linux-gnu, default)	43s
cross (stable, powerpc-unknown-linux-gnu, default)	35s
set-msrv / set-msrv	2s
minimal-versions / minimal-versions	40s
linux (x86_64-unknown-linux-gnu, 1.72.0)	39s
build (1.72.0, thumbv7em-none-eabi)	33s
linux (x86_64-unknown-linux-gnu, stable)	27s
macos (1.72.0)	31s
windows (x86_64-pc-windows-gnu, 1.72.0)	58s
build (1.72.0, wasm32-unknown-unknown)	20s
macos (stable)	24s
windows (x86_64-pc-windows-gnu, stable)	2m 9s
build (1.72.0, loongarch64-unknown-linux-gnu)	21s
build (stable, thumbv7em-none-eabi)	19s
build (stable, wasm32-unknown-unknown)	21s
build (stable, loongarch64-unknown-linux-gnu)	23s
	10m 57s

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