Track modified donations via transactions

[ivanb777]

Summary

This PR changes the approach to tracking modified donations to ensure consistency and accuracy. Instead of relying on the donation's updated_at, we now track donation modifications via transactions updates.

Key Changes

1. Modified Donations: Updates to donations are now driven by changes in related transactions, eliminating inconsistencies with the previous updated_at approach.
2. Refund Handling: Refunded transactions are now recorded as separate negative donations. Additionally, the original donation is marked with a refunded_at timestamp to keep record of the refund status.
3. Test Coverage: We’ve added the necessary tests for fetch_donation_updates to validate the donations sync behaviour.

For more info see the Asana issue.

[michael-gratton]

Hey, this is a much smaller change than I expected! Thanks heaps for adding those donation tests.

I am a little surprised that no changes except removing that one line from Donation.import was needed - will that actually pick up all the related things fine? Like ensure that refunds in Id are correctly related?

[ivanb777]

Hey @michael-gratton, thanks heaps for the feedback. I've taken them onboard, but went slightly differently re: import approach. The signature for instance import is changed, but the signature for the class method is the same – I've updated the logic to be compatible with what the instance method expects.

I am a little surprised that no changes except removing that one line from Donation.import was needed - will that actually pick up all the related things fine? Like ensure that refunds in Id are correctly related?

Yes, it's simple as that. The previous implementation didn't record the refunds, it just marked the corresponding refund_of_id donation as refunded. Yes, removing that line was necessary for refunds to also be recorded in addition to marking/timestamping the corresponding transaction with refunded_at. Although the implementation now has slightly changed.

[michael-gratton]

Think I'm pretty happy with this. Let's get this merged once the current batch of Id changes gets promoted to prod.