Add country package version to economy comparisons

[anth-volk]

Fixes #125.

What Changed

• Added a utility function to fetch the version of a given package in an environment
• Added a function to fetch the version of a policyengine country package based upon country ID
• Updated EconomyComparison schema to include country_package_version key
• Updated calculate_economy_comparison() to provide the country package version key as part of its returned EconomyComparison dict
• Added tests for utility functions

Why This Change

• Allows for passing of country package version value to workflow run output, simplifying downstream comparison of this and v1 workflow country package version

[mikesmit]

One opinionated comment, otherwise nitts or questions.

[anth-volk]

Update: tests fail due to a typo in the schema definition

[anth-volk]

Modifying based on review. Switching to draft until complete.

[mikesmit]

One opinionated comment, otherwise nitts or questions.