test: add equivalent tests using logProductAction for removed deprecated methods

Adds tests that replace removed logCheckout/logPurchase/logRefund tests
with equivalent coverage using logProductAction:
- Full DTO validation for purchase and refund events
- Badly formed ecommerce input sanitization
- Array of products support for purchase and refund
- Product position null handling
- Expand commerce events with/without summary total (plus-one)
- CustomFlags for checkout, purchase, and refund actions
- Native SDK bridge product list serialization (Android + iOS)
- Clarified expand test names with plus-one context comments

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rmi22186