Get a version from a refdate

[aecorn]

Description

The package has added ways of getting "the latest" version, but not "version from a certain date".

Here is some example code that solves this outside the package:

classification = klass.KlassClassification(klass_codelist)
    date_keyed: dict[datetime.datetime, VersionPartType] = {
        dateutil.parser.parse(version_part["validFrom"]): version_part
        for version_part in classification.versions
    }
    date_keyed_sorted_reversed = {k: date_keyed[k] for k in sorted(date_keyed)[::-1]}

    ver_final: None | VersionPartType = None
    ver_date: datetime.datetime
    for ver_date, ver in date_keyed_sorted_reversed.items():
        if ver_date <= refdate_datetime:
            ver_final = ver
            break

    if ver_final is None:
        raise KeyError(
            f"Couldnt find a version for classification {klass_codelist}, that matches refdate {refdate}."
        )
    ver_id: int = ver_final["version_id"]
    version = klass.KlassVersion(ver_id)