Clean up code with black, add tests workflow

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✅ Result of Pytest Coverage

---------- coverage: platform linux, python 3.9.10-final-0 -----------

Name	Stmts	Miss	Cover
src/urtypes/init.py	2	0	100%
src/urtypes/bytes.py	16	1	94%
src/urtypes/cbor/init.py	3	0	100%
src/urtypes/cbor/data.py	30	4	87%
src/urtypes/cbor/decoder.py	132	58	56%
src/urtypes/cbor/encoder.py	94	20	79%
src/urtypes/crypto/init.py	9	0	100%
src/urtypes/crypto/account.py	26	1	96%
src/urtypes/crypto/bip39.py	23	1	96%
src/urtypes/crypto/coin_info.py	25	1	96%
src/urtypes/crypto/ec_key.py	31	1	97%
src/urtypes/crypto/hd_key.py	139	8	94%
src/urtypes/crypto/keypath.py	55	1	98%
src/urtypes/crypto/multi_key.py	37	0	100%
src/urtypes/crypto/output.py	121	13	89%
src/urtypes/crypto/psbt.py	6	1	83%
src/urtypes/registry.py	32	3	91%
TOTAL	781	113	86%

~ 13 passed in 0.35s ~