feature(contract): Ownable Patter nof RsTokenContract

[anonfedora]

Description

This PR introduces a formal Ownable pattern to the RsTokenContract, enabling secure ownership management and the ability to update the authorized minter (the CertificateContract). This ensures that the token contract can adapt to upgrades in the certificate issuance logic without requiring a full token redeployment.

Requirements

• Implement transfer_ownership(new_owner: Address).
• Use require_auth() for owner-only actions.
• Add an only_owner helper to centralize authorization logic.
• Implement set_certificate_contract to allow updating the authorized minter.
• Update existing owner-only functions (update_uri, burn) to use the new pattern.

Closes #137

Changes

Contract Logic (token.rs)

• Ownership State: Added DataKey::Owner to manage the contract owner (initially set to the certificate_contract during init).
• Authorization Helpers:
  • only_owner: Standardized check that calls require_auth() and verifies the caller is the current owner.
  • check_owner: Internal helper for scenarios where require_auth() might have already been called (e.g., in burn).
• Administrative Functions:
  • transfer_ownership: Securely migrates ownership to a new address.
  • set_certificate_contract: Updates the address allowed to call mint and set_mint_pause.
• Refactoring:
  • Updated update_uri to use only_owner.
  • Updated burn to allow either the contract owner or the student to burn tokens using the new check_owner helper.

Clippy & Code Quality

• Fixed several unnecessary_cast warnings in lib.rs.
• Refactored a needless_range_loop in tests.rs to use idiomatic iterators.

Verification Results

Ran 24 unit tests in token::tests with 100% success rate:

• test_ownership_transfer: Verified successful migration and updated access control.
• test_set_certificate_contract: Confirmed the ability to rotate the authorized minter.
• test_unauthorized_ownership_transfer: Verified that non-owners cannot hijack the contract.
• owner_can_burn_student_tokens: Re-verified that administrative burning still works with the new owner state.

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[ayomideadeniran]

Pr under review.