feat(invoice-escrow): add multi-token escrow payment support

[Promzy204-bad]

• Fix duplicate discriminant 15 in errors.rs (Paused vs InvalidPayer); renumber InvalidPayer=16, InvalidDueDate=17, add TokenNotAccepted=18
• Add accepted_tokens Vec field to EscrowData in types.rs
• Update create_escrow to accept accepted_tokens param; validate list is non-empty and payment_token is a member; enforce ensure_not_paused
• Update fund_escrow to accept funding_token param; validate token against accepted_tokens; lock chosen token on first fund contribution
• record_payment and refund always use the locked-in data.token
• Fix Option IntoVal issues in invoke_contract calls (use .to_val())
• Emit accepted_tokens (as Val) in escrow_created event
• Update all existing tests to pass new function signatures
• Add 7 new multi-token unit tests covering: create with multi-token list, payment_token not in accepted list, empty accepted list, fund with accepted token, fund with rejected token, payment uses locked funding token, single-token backwards compat, accepted_tokens in created event

All 67 tests pass.

Description

Closes #

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📝 Documentation update
• 🎨 UI/UX improvement
• ♻️ Code refactoring
• ✅ Test addition or update
• 🔧 Configuration change

Checklist

• My code follows the code style of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Testing

How to Test

1. Step one
2. Step two
3. Step three

Test Coverage

• Unit tests added/updated
• Integration tests added/updated
• E2E tests added/updated (if applicable)
• Manual testing completed

Screenshots (if applicable)

Additional Notes

For Reviewers

• Code quality and readability
• Test coverage
• Security implications
• Performance impact
• Breaking changes
• closes [CONTRACTS] Invoice Escrow: Add Multi-Token Escrow Payment Support #79

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[chizzy192]

Hi @Promzy204-bad, please rebase on dev to resolve struct definition conflicts in contracts/invoice-escrow/src/types.rs where multi-token data structures overlap with recent storage refactors.