specifically name the lat,long columns `gtfs_travel_to_latitude/longitude` to note which gps point is referred to

one final suggestion: could specifically name the lat,long columns with something like `gtfs_travel_to_latitude/longitude` to communicate which gps point it refers to.

_Originally posted by @rymarczy in https://github.com/mbta/lamp/pull/542#pullrequestreview-3068653091_
            