Convert string properties to char strings in python mask creator

[xylar]

Previously, properties (e.g. height and history) for mask variables were being written out as string fields. These work for NETCDF4 format but cannot be converted with ncks to CDF format. Instead, we want to write them out as character strings in the same way that transect and region names are handled. This merge handles all fields that are strings in the same way, using the length of the longest string as the dimension of character fields. This retains compatibility with NETCDF3* formats.

The mask creator has also been updated to use the desired ruff formatting and to use f-strings instead of format strings.

[xylar]

Testing

This was tested as part of a workflow to create culled meshes in Polaris on Chrysalis. Without this fix, string variables caused the transect mask creator to fail during writing NetCDF fields using the CDF5 conversion technique in #633. With this fix, string variables are successfully written as character arrays, which then allows conversion to CDF5 to proceed as expected.