Adjust no-transact pop hashing mechanism

[CBroz1]

Description

Previous hashing mechanism used numpy arrays. Empty arrays can have unexpected hashes. This explicitly fetches the data from the tables to avoid a seeming error when populate is called in a table with an empty key_source

Checklist:

• No. This PR should be accompanied by a release: (yes/no/unsure)
• N/a. If release, I have updated the CITATION.cff
• No. This PR makes edits to table definitions: (yes/no)
• N/a. If table edits, I have included an alter snippet for release notes.
• No. If this PR makes changes to position, I ran the relevant tests locally.
• Yes. I have updated the CHANGELOG.md with PR number and description.
• N/a. I have added/edited docs/notebooks to reflect the changes