test: expand WooCommerce event coverage

[anyelopetit]

Summary

• Adds focused Pest coverage for WooCommerce event hooks and outbound request shape.
• Verifies product views, coupon redemption, cart add/remove/quantity changes, order placement, order status transitions, refunds, user registration, and deactivation cleanup.
• Switches order session meta handling to WooCommerce order CRUD methods for HPOS-safe reads/writes:
  • order placement writes session meta through $order->update_meta_data(...) and $order->save()
  • order status/refund tracking reads session meta through $order->get_meta(...)

Scope

• This PR improves WooCommerce event coverage and order session meta access patterns.
• It does not refresh Composer dependencies.
• It does not change CI or release packaging.
• It does not declare HPOS compatibility.
• HPOS compatibility declaration remains deferred until runtime smoke testing with HPOS enabled and disabled.

Validation

• composer install
• composer test
• composer format:check
• composer build

Verification

• composer test: passed
  • 47 tests
  • 142 assertions
• composer build: passed
• composer install: run afterward to restore dev dependencies
• composer format:check: passed after restoring dev dependencies

Notes

• Tests use WordPress/WooCommerce mocks and intercept wp_remote_request/wp_remote_post.
• No real Hellotext API calls are made.