Migrate contrib json tests to standard json test framework

[RahilJain1366]

Fixes #7520

[pavoljuhas]

LGTM after pushing in few small tweaks.
Thank you for taking care of this!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.38%. Comparing base (1deffd6) to head (bdd67f1).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7743   +/-   ##
=======================================
  Coverage   99.38%   99.38%           
=======================================
  Files        1091     1090    -1     
  Lines       97919    97920    +1     
=======================================
+ Hits        97313    97314    +1     
  Misses        606      606           

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[RahilJain1366]

Hi @pavoljuhas

Thank you for the tweaks and letting me contribute to the repo!

A quick doubt on why we are adding @value.value_equality(unhashable=True) in cirq-core/cirq/contrib/bayesian_network/bayesian_network_gate.py?

[pavoljuhas]

A quick doubt on why we are adding @value.value_equality(unhashable=True) in cirq-core/cirq/contrib/bayesian_network/bayesian_network_gate.py?

To avoid failure of hash_from_pickle_test.py such as here. That test reuses the list of JSON-tested classes to verify consistency of their hash(obj) after pickle serialization / deserialization. The test is skipped for unhashable classes hence the unhashable=True argument to make BayesianNetworkGate unhashable.