Epic (GTFS Schedule): Implement typecasting / type-checking and schema validity checks in views_staging

[lauriemerrell]

Inspired by #1148.

Right now, we don't check data types in a structured way in the GTFS schedule pipeline. In #1148 we were causing issues by setting data types in gtfs_schedule_history external table definitions that weren't actually checked or handled at all, so any violations caused a total pipeline failure.

The proper place to check and enforce data types is gtfs_views_staging where the _clean tables are created.

To do this, we should decide how to handle data type validations like what occurred in #1148 - as an interim there we just used SAFE_CAST so that the data made it into views with a null instead of the corrupt value.

• Should rows with illegal data types be dropped? Or should we pass the nulls through?
• If we drop rows, how do we want to handle the resulting foreign key violations?
• Are there other fields we want to CAST? Right now it's just stop lat/long.

[lauriemerrell]

looks like this created a dupe, closing