Switch @validate_country to decorator

[ldorner]

Overview

Currently, there is a repeated check and short-circuit in many functions to validate existence of the given country ID. This PR refactors validate_country as a decorator to DRY the code. We may consider transitioning this to a before_request hook to further reduce code repetition.

This is essentially a refactor. There should be no functional change.

Changes

• Update validate_country to change it into a decorator/wrapper
• Replace instances of validate_country() check & short circuit -> @validate_country decorator
• Add unit tests for the validate_country function
• Add a sanity test in test_policy.py to ensure that the decorator functionality works

[anth-volk]

Thank you for this work @ldorner. I will review probably tomorrow, depending on progress on some things I need to catch up on from some time off.

[ldorner]

I rebased to pull in recent changes/resolve conflicts.

[anth-volk]

@ldorner Unfortunately, it looks like the added test still fails due to accessing the keys() attribute of a tuple, which does not possess them.

[ldorner]

@ldorner Unfortunately, it looks like the added test still fails due to accessing the keys() attribute of a tuple, which does not possess them.

Sorry! Bad merge. Fixed now :)

[anth-volk]

@ldorner Thanks again for this, will review early tomorrow