Simplify the internal data structures in Ciclops

[jsilvela]

The crux of Ciclops, internally, is the test_summary data structure.
It is computed with a single traversal through the directory where the test artifacts
are held.
Each test file contains a single test execution in a single platform-k8s-postgres.
Each is ingested by a function that then updates the test_summary as a side effect.

This is how the test_summary looks overall.

    {
        "total_run": 0,
        "total_failed": 0,
        "total_special_fails": 0,
        "by_test": { … },
        "by_code": { … },
        "by_special_failures": { … },
        "by_matrix": { … },
        "by_k8s": { … },
        "by_platform": { … },
        "by_postgres": { … },
        "test_durations": { … },
        "suite_durations": { … },
    }

internally, the by_XYZ dictionaries contain, within them, something like

    by_test = {
        "total": {},
        "failed": {},
        "k8s_versions_failed": {},
        "pg_versions_failed": {},
        "platforms_failed": {},
    }

And inside of each of these dictionaries, the element in question will be the key.
E.g. the test name, in the dictionary above, after a few iterations, we could have something like

    by_test = {
        "total": {
            "test A": 12,
            "test B", 10,
        },
        "failed": {
            "test A": 2,
            "test B", 1,
        },
        "k8s_versions_failed": {
            "test A": {
                "1.26": True,
                "1.27": True,
            },
            "test B": {
                "1.26": True,
            }
        },
        ...
        ...
    }

The above structure gets difficult to reason about.
It would be a lot more understandable to use the following representation.

    by_test = {
        "test A": {
            "total": 12,
            "failed": 2,
            "k8s_versions_failed": ["1.26", "1.27"],
            ...
        },
        "test B": {
            "total": 10,
            "failed": 1,
            "k8s_versions_failed": ["1.26"],
            ...
        },
        ...
        ...
    }