Add pause then cancel then restore round-trip lifecycle test #589

Description

Exercise a full round-trip through Paused, Cancelled, and Restored states to confirm state-machine transitions, metadata preservation, and secondary-index consistency after each hop.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Relevant code: contracts/subscription_vault/src/subscription.rs
• Test lives in contracts/subscription_vault/src/test_lifecycle_roundtrip.rs

Suggested execution

• Fork the repo and create a branch
• git checkout -b tests/lifecycle-roundtrip
• Implement changes
  • Drive create -> pause -> cancel -> restore
  • Assert secondary index membership after each step
  • Assert emitted events in order
• Validate security and correctness assumptions

Test and commit

• Run tests
  • cargo test --all
• Cover edge cases
  • Restore after long dormancy, restore with expired metadata TTL, and repeat round-trip
• Include test output and security notes

Example commit message

test: lifecycle round-trip pause/cancel/restore

Guidelines

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 96 hours