Replace pysha3 with pycryptodomex

pysha3 is not maintained anymore and it doesn't build correctly with
Python 3.11 so replace it with pycryptodomex that is still maintained and
working correctly with new python versions

opentimestamps/core/op.py

@@ -10,8 +10,8 @@
 # in the LICENSE file.
 
 import binascii
+import Cryptodome.Hash.keccak
 import hashlib
-import sha3
 import opentimestamps.core.serialize
 
 class MsgValueError(ValueError):
@@ -344,6 +344,6 @@ class OpKECCAK256(UnaryOp):
     DIGEST_LENGTH = 32
 
     def _do_op_call(self, msg):
-        r = sha3.keccak_256(bytes(msg)).digest()
+        r = Cryptodome.Hash.keccak.new(digest_bits=256, data=bytes(msg)).digest()
         assert len(r) == self.DIGEST_LENGTH
         return r

requirements.txt

@@ -1,3 +1,3 @@
 python-bitcoinlib>=0.9.0,<0.12.0
 GitPython>=2.0.8
-pysha3>=1.0.2
+pycryptodomex>=3.3.1

setup.py

@@ -70,7 +70,7 @@
     # requirements files see:
     # https://packaging.python.org/en/latest/requirements.html
     install_requires=['python-bitcoinlib>=0.9.0,<0.12.0',
-                      'pysha3>=1.0.2'],
+                      'pycryptodomex>=3.3.1'],
 
     # List additional groups of dependencies here (e.g. development
     # dependencies). You can install these using the following syntax,