Time mapper doesn't handle time zones from dsgrid

dsgrid creates geography records with time zones like EasternPrevailing, CentralPrevailing, etc: https://github.com/dsgrid/dsgrid-project-StandardScenarios/blob/main/dsgrid_project/dimensions/counties.csv

chronify uses pandas for time zone conversions and doesn't know about these. What should we do?

E               pytz.exceptions.UnknownTimeZoneError: 'PacificPrevailing'

env/lib/python3.11/site-packages/pytz/__init__.py:188: UnknownTimeZoneError
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> entering PDB >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> PDB post_mortem (IO-capturing turned off) >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> /Users/dthom/repos/secondary-dsgrid/env/lib/python3.11/site-packages/pytz/__init__.py(188)timezone()
-> raise UnknownTimeZoneError(zone)
(Pdb) up
> /Users/dthom/repos/secondary-dsgrid/timezones.pyx(170)pandas._libs.tslibs.timezones.maybe_get_tz()
(Pdb) 
> /Users/dthom/repos/secondary-dsgrid/timezones.pyx(145)pandas._libs.tslibs.timezones.maybe_get_tz()
(Pdb) 
> /Users/dthom/repos/secondary-dsgrid/env/lib/python3.11/site-packages/pandas/core/arrays/datetimes.py(911)tz_convert()
-> tz = timezones.maybe_get_tz(tz)
(Pdb) 
> /Users/dthom/repos/secondary-dsgrid/env/lib/python3.11/site-packages/pandas/core/indexes/datetimes.py(283)tz_convert()
-> arr = self._data.tz_convert(tz)
(Pdb) 
> /Users/dthom/repos/secondary-dsgrid/env/lib/python3.11/site-packages/pandas/core/indexes/accessors.py(132)_delegate_method()
-> result = method(*args, **kwargs)
(Pdb) 
> /Users/dthom/repos/secondary-dsgrid/env/lib/python3.11/site-packages/pandas/core/accessor.py(112)f()
-> return self._delegate_method(name, *args, **kwargs)
(Pdb) 
> /Users/dthom/repos/chronify/src/chronify/representative_time_range_generator.py(64)create_tz_aware_mapping_dataframe()
-> dft["timestamp_tmp"] = dft[timestamp_col].dt.tz_convert(tz)
(Pdb) ll
 54  	   def create_tz_aware_mapping_dataframe(
 55  	       self,
 56  	       df: pd.DataFrame,
 57  	       timestamp_col: str,
 58  	       time_zones: list[str],
 59  	   ) -> pd.DataFrame:
 60  	       """Create time zone-aware time mapping dataframe."""
 61  	       dfm = []
 62  	       for tz in time_zones:
 63  	           dft = df.copy()
 64  ->	           dft["timestamp_tmp"] = dft[timestamp_col].dt.tz_convert(tz)
 65  	           dft = self._handler.add_time_attribute_columns(dft, "timestamp_tmp")