test: add adversarial coverage for list_offerings in lib

[MuhammadDG]

Overview

This PR adds focused adversarial test coverage for the list_offerings contract method in src/lib.rs. The new test module exercises valid calls, boundary and invalid inputs for env: Env, issuer: Address, and namespace: Symbol, verifies unauthorized-caller behavior where relevant, and asserts that state is unchanged after rejected operations.

Related Issue

Changes

🧪 Adversarial tests for list_offerings

• [ADD] src/test_offering_count_adversarial.rs
  • Focused test module targeting list_offerings in src/lib.rs.
  • Covers the happy path (valid env, issuer, namespace) to confirm the public contract is preserved.
  • Exercises boundary and invalid inputs for issuer: Address and namespace: Symbol (e.g. unknown issuer, empty/unknown namespace).
  • Exercises unauthorized-caller paths where the contract enforces authorization.
  • Asserts that rejected operations leave stored state unchanged, and that error/boundary behavior is deterministic and observable.
  • No changes to the public contract of list_offerings; tests only.

Verification Results

cargo test test_offering_count_adversarial
✅ focused adversarial suite passed

cargo test
✅ surrounding suite passed

cargo clippy --all-targets -- -D warnings
✅ no warnings

cargo build
✅ build succeeded

Acceptance Criteria	Status
Cover the named behavior with focused automated tests, including the relevant success and failure paths	✅ Valid, boundary, invalid, and unauthorized paths covered in src/test_offering_count_adversarial.rs
Preserve the existing public contract unless the change includes an explicit compatibility plan	✅ No contract changes; tests only
Make error and boundary behavior observable and deterministic	✅ Rejected operations assert deterministic errors and unchanged state

Closes #1075