`pydsstools` engine does not support `write_rts`

[dwr-zroy]

The feature is currently not supported. No technical issues are known to stand in the way, but the development has not been motivated.

This gap currently causes this failure in the test suite:

temporary_dss = WindowsPath('C:/Users/zroy/Documents/_Python/pandss/tests/assets/created/uUnKGxlXYf.dss')
request = <FixtureRequest for <Function test_copy_multiple_rts_6[dss_7]>>

    @pytest.mark.parametrize("dss", ("dss_6", "dss_7"))
    def test_copy_multiple_rts_6(dss, temporary_dss, request: FixtureRequest):
        dss = request.getfixturevalue(dss)
        p_old = (
            "/CALSIM/MONTH_DAYS/DAY//1MON/L2020A/",
            "/CALSIM/PPT_OROV/PRECIP//1MON/L2020A/",
        )
        p_new = (
            "/CALSIM/MONTH_DAYS/DAY//1MON/L2020A/",
            "/CALSIM/PPT_OROV/PRECIP//1MON/L2020A/",
        )
        with catch_warnings(action="error"):
>           pdss.copy_multiple_rts(dss, temporary_dss, tuple(zip(p_old, p_new)))

tests\test_rts.py:252: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
src\pandss\utils.py:150: in copy_multiple_rts
    DST.write_rts(dst_path, SRC.read_rts(src_path))
src\pandss\dss.py:243: in write_rts
    return self.engine.write_rts(path, rts)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <pandss.engines.pydsstools_engine.PyDssToolsEngine object at 0x000001958C713450>
path = DatasetPath(a='CALSIM', b='MONTH_DAYS', c='DAY', d='.*', e='1MON', f='L2020A')
rts = RegularTimeseries(path=DatasetPath(a='CALSIM', b='MONTH_DAYS', c='DAY', d='.*', e='1MON', f='L2020A'), values=array([-...09-30T23:59:59.000000'],
      dtype='datetime64[us]'), period_type='PER-AVER', units='DAYS', interval=<Interval 1MON>)

    def write_rts(self, path: DatasetPath, rts: RegularTimeseries):
        """Writes a single regular timeseries to a DSS file."""
>       raise NotImplementedError(
            f"write_rts not implemented on {self.__class__.__name__}"
        )
E       NotImplementedError: write_rts not implemented on PyDssToolsEngine

src\pandss\engines\__init__.py:45: NotImplementedError