Test Suite Refactor

[f-allian]

• [Low priority] Currently running our test suite locally runs into several hundreds of warnings, which needs investigating. Also, profiling our test execution duration will also help identify any hotspots (likely not many but it'll be good to flesh them out).

[f-allian]

================================================================================= warnings summary ==================================================================================

causal_testing/specification/causal_dag.py:142: 1 warning
examples/covasim_/doubling_beta/example_beta.py: 7 warnings
examples/lr91/example_max_conductances.py: 66 warnings
examples/lr91/example_max_conductances_test_suite.py: 1 warning
examples/poisson/example_run_causal_tests.py: 1 warning
tests/json_front_tests/test_json_class.py: 18 warnings
tests/specification_tests/test_causal_dag.py: 27 warnings
tests/specification_tests/test_metamorphic_relations.py: 14 warnings
tests/surrogate_tests/test_causal_surrogate_assisted.py: 5 warnings
tests/testing_tests/test_causal_test_adequacy.py: 5 warnings
tests/testing_tests/test_causal_test_case.py: 8 warnings
tests/testing_tests/test_causal_test_suite.py: 3 warnings