Fix geo_id type in read_geos...() function family

[allenbaron]

This pull request ensures that joins on geo_id between geos datasets and other datasets work without an intermediate step to convert geo_id to character.

I'd like to merge this into main and then rebase the dev branch onto it, if no one is editing the dev branch. Otherwise, we should just merge this to both the main and dev branches.

Problem:
Type of 'geo_id' variable in geos datasets is not set;
it is sometimes of type integer and other times of type character.
In non-geos datasets (demographics, land area, etc.) 'geo_id' is
always of type character.

Fix:
Update all functions to coerce 'geo_id' to character when read.