[Idrhas]

Description

This PR addresses and fixes a critical issue with the reentrancy guard implementation and extends its protection to all applicable state-changing functions across the contract.

closes #11

Changes Made

• Fixed Lock Persistence Bug: Switched the storage type in reentrancy.rs from persistent() to instance(). This ensures that if a guarded function panics, the lock is automatically cleared at the end of the transaction rather than permanently bricking the contract functions.
• Expanded Guard Coverage: Added reentrancy::enter(env) and reentrancy::exit(env) to the following unprotected state-changing functions:
  • register_merchant (merchant.rs)
  • create_invoice (invoice.rs)
  • pause and unpause (pausable.rs)
  • grant_role and revoke_role (access_control.rs)
• Comprehensive Testing: Added a dedicated test suite (test_reentrancy.rs) to verify that the low-level locking works properly and that attempting re-entrant calls into guarded functions correctly results in an Error(Contract, #4) panic.

Testing

• All 33 unit tests pass successfully in the wasm32-unknown-unknown environment, including the newly added mock reentrancy scenarios.