closea #92 feat: add tri-state anchor_status read for anchor lifecycle tracking

[emmyoat]

Summary

Adds an anchor_status(env, anchor) -> AnchorStatus read function to distinguish between addresses that have never been registered, addresses that are currently active, and addresses that were previously registered and later deregistered.

is_anchor returns a single boolean and cannot distinguish between "never registered" and "previously registered then deregistered". This tri-state distinction allows off-chain services (frontend detail page and backend sync logic) to query anchor registration lifecycle status directly from the contract.

Key Changes

• src/types.rs: Added AnchorStatus enum with variants NeverRegistered, Active, and Deregistered.
• src/storage.rs: Implemented anchor_status reader that checks persistent storage:
  • None $\rightarrow$ AnchorStatus::NeverRegistered
  • Some(true) $\rightarrow$ AnchorStatus::Active (with TTL bump)
  • Some(false) $\rightarrow$ AnchorStatus::Deregistered (with TTL bump)
• src/lib.rs: Re-exported AnchorStatus and exposed AnchornetContract::anchor_status.
• src/test.rs: Added test_anchor_status_lifecycle and test_anchor_status_read_bumps_ttl.
• README.md: Updated contract interface table with anchor_status(anchor).

Backward Compatibility

is_anchor and all existing contract callers remain completely unaffected.

Checklist

• Tri-state status distinguishing all three states correctly implemented.
• Existing is_anchor behavior and callers unaffected.
• Full test coverage added in src/test.rs.
• Documented in README.md.