Moved and renamed hash256 from util.py to zmq_interface.py (Elichai Turkel)
Pull request description:
Right now there are two `hash256(bytes)` in the test framework:
first: https://github.com/bitcoin/bitcoin/blob/master/test/functional/test_framework/util.py#L186
second: https://github.com/bitcoin/bitcoin/blob/master/test/functional/test_framework/messages.py#L60
While they have the same name they're actually doing different things, one just does a sha256d and the other sha256d and reverses the bytes.
so I renamed the second one to be `hash256r` to signify that it's hash256 reversed.
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Backport of Core [[https://github.com/bitcoin/bitcoin/pull/16598 | PR16598]]