Fix Time_period cast to String does not follow the time_period_output_format

[mla2001]

Initial Checks

• I have searched existing issues for duplicates
• I have read the documentation

Summary

Time_period cast to String shows the Time_Period internal representation as string instead of the time_period_output_format.

Reproducible Example

script = """
        DS_str := DS_1[calc Me_2 := cast(Me_1, string)];
        DS_filtered := DS_str[filter Me_2 = "2021"];
        Data_in_2022 <- DS_filtered[drop Me_2];
    """

    data_structures = {
        "datasets": [
            {
                "name": "DS_1",
                "DataStructure": [
                    {"name": "Id_1", "type": "Integer", "role": "Identifier", "nullable": False},
                    {"name": "Me_1", "type": "Time_Period", "role": "Measure", "nullable": True},
                ],
            }
        ]
    }

    data_df = pd.DataFrame({"Id_1": [1, 2, 3], "Me_1": ["2020", "2021", "2022"]})

    datapoints = {"DS_1": data_df}

    run_result = run(
        script=script,
        data_structures=data_structures,
        datapoints=datapoints,
        time_period_output_format="natural",
    )

vtlengine version

1.6.2

Python version

Any

OS

Any