Fuzz

Backport #809 to 0.10.x #430

Job	Run time
fuzz (compile_descriptor)	1s
fuzz (parse_descriptor)	1s
fuzz (roundtrip_miniscript_script)	1s
fuzz (parse_descriptor_secret)	1s
fuzz (roundtrip_descriptor)	1s
fuzz (roundtrip_semantic)	1s
fuzz (roundtrip_concrete)	1s
fuzz (roundtrip_miniscript_str)	1s
verify-execution	0s
	8s

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