Fix: add Network::BitcoinMainnet and Network::BitcoinTestnet #23

Job	Run time
fuzz (bitcoin_deserialize_address)	1m 59s
fuzz (bitcoin_deserialize_amount)	1m 47s
fuzz (bitcoin_deserialize_block)	1m 51s
fuzz (bitcoin_deserialize_prefilled_transaction)	1m 45s
fuzz (bitcoin_deserialize_psbt)	1m 59s
fuzz (bitcoin_deserialize_script)	2m 1s
fuzz (bitcoin_deserialize_transaction)	1m 17s
fuzz (bitcoin_deserialize_witness)	2m 18s
fuzz (bitcoin_deser_net_msg)	1m 55s
fuzz (bitcoin_outpoint_string)	1m 59s
fuzz (bitcoin_script_bytes_to_asm_fmt)	2m 0s
fuzz (hashes_cbor)	2m 3s
fuzz (hashes_json)	1m 55s
fuzz (hashes_ripemd160)	1m 58s
fuzz (hashes_sha1)	2m 5s
fuzz (hashes_sha256)	1m 49s
fuzz (hashes_sha512_256)	1m 57s
fuzz (hashes_sha512)	1m 50s
verify-execution	0s
	34m 28s

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