Fix localhost domain issue in economically unviable refund emails

Updated economically unviable refund email notifications to use create_shop_context_request() instead of passing env_request directly or creating DummyRequest objects. This ensures emails are sent from the proper shop domain instead of localhost.

Fixed in:

• Expired payment processing (line ~2147)
• Underpayment processing (line ~2911)
• Passive monitoring refund retries (line ~3290)

Note: Duplicate payment processing was already correct.

Summary by CodeRabbit

• Bug Fixes
  • Purchase and refund emails now consistently use the correct shop domain and links.
  • Improved handling of overpayments, underpayments, expired invoices, and out-of-stock scenarios to ensure accurate notifications.
  • Email sending is attempted only when required invoice and user details are available, reducing missed or misrouted messages.
  • Greater consistency across duplicate-payment flows, reducing confusion in payment status emails.