Add comprehensive tests for multi-output transaction tracking defect fix

This adds complete test coverage for the critical fix where multi-output refund transactions now set both refund_tx_hash AND swept_tx_hash to prevent re-sweeping already swept payments.

Key test scenarios covered:

• Multi-output refund transaction creation (XMR and DOGE)
• Shop sweep amount calculation: max(0, received_amount - refund_amount)
• Prevention of double-sweep attempts when swept_tx_hash is already set
• Same transaction hash handling for both refund and sweep monitoring
• Real-world defect scenario using actual transaction hash from logs
• Edge cases including full refunds and negative amount protection

The tests validate that the "insufficient funds" error has been resolved by ensuring payments with existing swept_tx_hash are not swept again.

Summary by CodeRabbit

• New Features
  • Improved tracking for multi-output refund transactions, recording both refund and shop-sweep details with clearer event logs.
• Bug Fixes
  • Prevents double-sweeping when a sweep has already occurred.
  • More accurate Monero confirmation checks for specific accounts/subaddresses.
• Documentation
  • Added “Cryptocurrency RPC Access” guidance for Monero and Dogecoin.
  • Expanded “UUID Objects” section with usage tips and examples.
• Tests
  • Added comprehensive tests covering multi-output refunds, sweep accounting, and XMR/DOGE edge cases.
• Style
  • Minor formatting and string style consistency updates.