Mock contracts and test cabinet

[anxolin]

This PR mocks the ConditionalOrders tests, so we can run some unit tests that involves calls to the contract.

The new methods, like poll and cabinet will require this mocking.

This PR also adds the unit test for the cabinet

[github-actions]

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[coveralls]

coverage: 73.219% (+0.6%) from 72.617% when pulling 1525759 on test-cabinet into 4fcd0cc on main.