aa7a898c23 doc: use testnet4 in developer docs (Sjors Provoost)
6c217d22fd test: use testnet4 in argsman test (Sjors Provoost)
7c200ece80 test: use testnet4 in key_io_valid.json (Sjors Provoost)
d424bd5941 test: drop unused testnet3 magic bytes (Sjors Provoost)
8cfc09fafe test: cover testnet4 magic in assumeutxo.py (Sjors Provoost)
4281e3603a zmq: use testnet4 in zmq_sub.py example (Sjors Provoost)
Pull request description:
In preparation for dropping testnet3 entirely in #31974 this PR migrates a few things to testnet4:
* the ZMQ examples
* developer docs
* various unit tests
* the snapshot magic byte check in `feature_assumeutxo.py`
It drops `testnet3` from `MAGIC_BYTES` in the test framework, since no test uses it.
ACKs for top commit:
fjahr:
re-ACK aa7a898c23
maflcko:
lgtm ACK aa7a898c23🔊
hodlinator:
re-ACK aa7a898c23
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