fix: repair corrupted test files and update call signatures

[Ayilojay]

• Reconstruct invoice_test.rs: remove interleaved/duplicated content, fix test_release_escrow_transitions_paid_to_released body, deduplicate test_mark_paid_blocked_when_paused, fix test_invoice_create_to_*
• Add &0 merchant_nonce arg to all create_invoice calls in invoice_id_boundary_test, invoice_invalid_amount_test, invoice_amount_invariant_test, and invoice_status_settlement_proposal_integration_test
• Add MaybeBytes import to tests that now use it
• Fix execute_settlement calls in treasury_threshold_rejection_test to include missing signer argument
• Fix task1_tests event_symbol: use TryFromVal::try_from_val(env, &val) instead of .try_into() which has no Env context
• Update property test cases to use amounts >= 10_000_000 (1 USDC min) to satisfy the require_usdc_precision guardrail added in test(treasury): paused treasury rejects all state-mutating calls #57
• Fix test_amount_matrix: remove (1, 1, true) case now rejected by USDC precision check
• Fix u64 boundary tests to use try_ variants to avoid non-unwinding host aborts at u64::MAX
• Create abis/invoice.json ABI snapshot with all 13 functions and 8 events to satisfy test_abi_snapshot_matches_contract

Description

Related Issue

Closes #[issue_id]

Checklist

• Description of changes included
• Test coverage confirmation (new/updated tests added)
• Screenshot/gif for UI changes (if applicable)
• ABI snapshot regenerated (if contract interface changed)
• just check passing locally
  Closes #84: Integration test — compliance block between proposal and execution #275
  Closes #85: Extend pause-blocking integration coverage to the full lifecycle #276

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