Pytest folder naming update

[nghielme]

Description

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This PR updates pytest test naming conventions across the hls4ml test suite, it address the issue #1436:

• Adds utility functions in conftest.py for generating unique test case identifiers in pytest
• Updates test parametrization across 60+ test files to use consistent naming patterns
• Renames synthesis output JSON files to follow the new naming convention (e.g., test_activations-elu-Vitis-io_parallel.json instead of older patterns)

The motivation is to improve test discoverability, reduce naming conflicts, and make test output more readable when running subsets of tests.

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Tests

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Test Configuration:

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[marco66colombo]

Thanks for the PR, the naming consistency goal is very helpful.

One comment: fixtures in conftest.py are auto-discovered by pytest, so with fixtures there’s no need to import helpers from conftest.py directly.
Pytest best practice is to expose helpers as fixtures (e.g., case_id) instead of importing from conftest.py.

A possible alternative solution could be adding a fixture like:

# conftest.py
@pytest.fixture
def case_id(request):
    return get_pytest_case_id(request)

Then use it where needed:

def test_dense(case_id, backend, io_type):
    ... 
    output_dir = str(test_root_path / case_id)
    ...

[marco66colombo]

On this job failure:

FAILED test_keras_api.py::test_activations[io_parallel-Vivado-activation_function2]
Baseline file .../test_keras_api_test_activations_io_parallel-Vivado-activation_function2.json not found

It looks like this specific baseline file (the activation_function2 one) is missing. The naming is consistent between the test output and the new baseline names, but that single file isn’t present, so the job fails (If I didn't miss anything). It also happens for other tests cases.
Probably the 2 is skipped and it goes 0,1,3,4,5. I think this is also why the assertions fail (the baseline 3 refers to actual test case 2 and so one, basically they're shifted by one).

Also, while digging into this I realized that the new names rely on pytest’s auto‑generated param IDs when the parameters are objects (like Keras layer instances). That’s why we get activation_function0/1/2/... instead of names like relu, elu, p_re_lu. If you want more readable names (and keep same behavior as for the old baseline names), it's possible to add explicit ids=:

@pytest.mark.parametrize(
    "activation_function",
    [...],
    ids=["relu", "leaky_relu", "elu", "p_re_lu", "sigmoid"],
)