test: check for all possible OP_CLTV fail reasons in feature_cltv.py (BIP 65) #19801

The functional test for BIP65 / OP_CHECKLOCKTIMEVERIFY (feature_cltv.py) currently only tests one out of five conditions that lead to failure of the op-code -- by prepending the script OP_1NEGATE OP_CHECKLOCKTIMEVERIFY OP_DROP to a tx's first input's scriptSig, the case of "the top item on the stack is less than 0" is checked:

https://github.com/bitcoin/bitcoin/blob/f8462a6d2794be728cf8550f45d19a354aae59cf/test/functional/feature_cltv.py#L26-L35

This PR adds the other cases (5 in total) by taking an integer argument to the function cltv_invalidate that is called in a loop instead of only once per testing scenario. Here is the full list of failure conditions and how they are tested (note that the scriptSig should still be valid before activation of BIP65, when OP_CLTV is simply a no-op):

• the stack is empty ➡️ prepending OP_CHECKLOCKTIMEVERIFY to scriptSig
• the top item on the stack is less than 0 ➡️ prepending OP_1NEGATE OP_CHECKLOCKTIMEVERIFY OP_DROP to scriptSig
• the lock-time type (height vs. timestamp) of the top stack item and the nLockTime field are not the same ➡️ prepending OPNum(1000) OP_CHECKLOCKTIMEVERIFY OP_DROP to scriptSig ➡️ setting tx.vin[0].nSequence=0 and tx.nCheckTimeLock=1296688602 (genesis block timestamp)
• the top stack item is greater than the transaction's nLockTime field ➡️ prepending OPNum(1000) OP_CHECKLOCKTIMEVERIFY OP_DROP to scriptSig ➡️ setting tx.vin[0].nSequence=0 and tx.nCheckTimeLock=500
• the nSequence field of the txin is 0xffffffff ➡️ prepending OPNum(500) OP_CHECKLOCKTIMEVERIFY OP_DROP to scriptSig ➡️ setting tx.vin[0].nSequence=0xffffffff and tx.nCheckTimeLock=500

The first commit creates a helper function for the tx modification and also includes some tidying up like turning single-line to multi-line Python imports where necessary and cleaning up some PEP8 warnings. The second commit prepares the invalidation function cltv_invalidate and the third and the fourth use it and check for the expected reject reason strings ("Operation not valid with the current stack size", "Negative locktime" and "Locktime requirement not satisfied").

<!--e57a25ab6845829454e8d69fc972939a-->

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

<!--174a7506f384e20aa4161008e828411d-->

Conflicts

No conflicts as of last run.

concept ACK

Rebased on master.

Rebased on master again.

Rebased on master.

Concept ACK

review ACK b01cd9471f435bb36b8ed5211a56baad51111ad2 🐣

<details><summary>Show signature and timestamp</summary>

Signature:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

review ACK b01cd9471f435bb36b8ed5211a56baad51111ad2 🐣
-----BEGIN PGP SIGNATURE-----

iQGzBAEBCgAdFiEE+rVPoUahrI9sLGYTzit1aX5ppUgFAlwqrYAACgkQzit1aX5p
pUiGwwv/ehsKGNFfYIyNn3Pb7H8mC7j6SfFijNHeg+rDldGw1lNA3MLjMvPGhs4v
+uuAbS74JCv4T6fEjw8K4ODx6ZU/+fyckT8HL2Qxx9TbqPN9+3Gc5Ww68137+RRW
mOzNy1S4Z6MPu3OtBZxkHSKHXPKF6sSTDyqjrxgslpOFNDceirBIahFTHPXy2geh
gZYLsQYtbY0kDJBLcfCh4vvPW5IpLO2Cr5iRQkVmj31upzvYniKmWtuCwmwrXZG9
mAKP0o9AGnfYWCufH1NpDBp4/JBrRITk+nz0bOgxYO99FiJMalX+YTP6xlkOIGgI
ChrXmz7/qe3FXypz9lA+hL44R7/ApLWhCfc4oK9bbHwSVqbjnTh5V20+EjYSK3ER
5IPjBDjbTN1768iQMRIjq2Aj9zQFrVwCkzlW56zwlECZoFHGEzDOWimHkVWd1vZR
qSvVIya8GmuqwWpEASi9O5yXArtqF+Vzr7s9Ki8TiTbGFOQFFlNFLgTXkOXi4Mrr
DC1R6djf
=TLhB
-----END PGP SIGNATURE-----

Timestamp of file with hash 0aea310db82e5dcfdbcc25d7e801d24635a1a608c8b997bbb98494c524f90747 -

</details>

Reworked the test some more in #21754