Refactor: update meta persistence in donor and donation repositories

[jonwaldstein]

Partially Resolves GIVE-2075

Description

This updates our donor and donation repositories to use the native WP meta functions for adding meta instead of directly inserting using SQL.

Before this, we were innocently deviating from how WordPress stores meta values, effectively bypasses some of the extra filters/sanitization of values. This resulted in problems downstream when retrieving the data.

So the lesson learned here is to always use the native WordPress api functions for storing and retrieving meta 😄.

Affects

• Creating new donations and donors (v2 and v3 forms)

Visuals

Testing Instructions

Make sure both v2 and v3 forms are working as expected.

• Create donation using v3 form and make sure core blocks/fields and custom fields are processing correctly
• Check the confirmation page, donation and donor details to make sure
• Repeat for v2 forms

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[kjohnson]

LGTM. Nice and straightforward PR with tests 🙌🏻

[kjohnson]

Build for QA, see https://github.com/impress-org/givewp/actions/runs/12815846433.