Add hex-encoding examples based on `base16ct` #989

Job	Run time
minimal-versions / minimal-versions	30s
set-msrv / set-msrv	5s
test (1.71.0)	35s
build (1.71.0, thumbv7em-none-eabi)	25s
test (stable)	23s
build (1.71.0, wasm32-unknown-unknown)	22s
build (stable, thumbv7em-none-eabi)	32s
build (stable, wasm32-unknown-unknown)	22s
	3m 14s

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