feat: implement view functions and event updates for issues #595-#598

[kaivegascod-a11y]

Summary

This PR implements solutions for four related GitHub issues:

Issue #598: Add invoice_id to invoice_refunded event data

• Modified the invoice_refunded event to include invoice_id in the event data tuple
• Makes it easier for indexers that decode only event data (not topics) to correlate refund events with invoices

Issue #597: Add get_invoice_amounts view function

• New public function to query invoice recipient amounts without retrieving the entire invoice structure
• Enables recipients and payers to easily determine individual entitlements without loading full invoice data
• Improves query efficiency and user experience

Issue #596: Add get_contract_paused view function

• New public function that allows off-chain clients and integrations to query contract pause state
• Enables trustless discovery of the pause state
• No authentication required

Issue #595: Add comprehensive tests for get_platform_fee_bps

• The function already exists in the codebase
• This PR adds comprehensive unit tests verifying the function returns correct platform fee basis points

Test Coverage

All implementations include comprehensive unit tests verifying:

• Correct return values for various inputs
• Edge cases (single recipient, multiple recipients, invalid IDs)
• Initial default states
• State changes after operations (pause/unpause)

Closes #598
Closes #597
Closes #596
Closes #595

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