Add hex-encoding examples based on `base16ct` #619

Job	Run time
minimal-versions / minimal-versions	39s
set-msrv / set-msrv	5s
test (1.71.0)	45s
build (1.71.0, thumbv7em-none-eabi)	26s
test (stable)	33s
build (1.71.0, wasm32-unknown-unknown)	24s
build (stable, thumbv7em-none-eabi)	23s
build (stable, wasm32-unknown-unknown)	16s
	3m 31s

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