- Rename `getMerchantByRegisterRef` to `inquiryMerchantByRef` and update associated response models for consistency.
- Implement `inquiryMerchantByKey` and `ABAInquiryMerchantByKeyRequestModel` to support credential inquiries via existing merchant keys.
- Remove the unused `merchantId` parameter from `ABAPayway` and `ApiService` initializers.
- Refactor `opensslEncrypt` to accept `String` inputs instead of `Map`, ensuring proper JSON encoding before encryption.
- Update `generateHash` utility to use `publicKey` as the HMAC key instead of `partnerId`.
- Expand the example application and `README.md` to demonstrate new registration and inquiry flows.
- Bump package version to `0.0.1-beta.2` and update `CHANGELOG.md`.