feat: refactor integration test db instantiation

[cylewitruk]

Description

The integration-env completely broke for me causing me to be unable to run integration tests locally and I'm not sure what the root cause actually was, but I kept getting a lot of failures with errors that looked like concurrency issues (despite that we're using single-threaded). It seemed to be related to creating databases using a template 🤷

This refactor fixed the issues for me anyway and simplifies the code a bit.

Changes

• Now uses a sequence in the database for db_num.
• The new_test_database() method is now a bit more streamlined -- I removed the parameters since we never use them, and it's now much simpler/smaller.

Testing Information

Checklist:

• I have performed a self-review of my code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules