Fuzz

Use `bech32` to calculate descriptor checksums #221

Job	Run time
fuzz (roundtrip_miniscript_str)	6m 22s
fuzz (roundtrip_miniscript_script)	7m 46s
fuzz (parse_descriptor)	6m 31s
fuzz (roundtrip_semantic)	6m 22s
fuzz (parse_descriptor_secret)	6m 43s
fuzz (roundtrip_descriptor)	6m 16s
fuzz (roundtrip_concrete)	6m 6s
fuzz (compile_descriptor)	6m 18s
verify-execution	7s
	52m 31s

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