refactor(account-lib): use Signature type

[bhavidhingra]

This pull request introduces several enhancements and new features to the SDK, focusing on improvements to message handling and support for the CIP8 standard. Key changes include adding support for serialized signatures in EIP-191 messages, implementing the CIP8 message standard for Cardano, and extending the test suite to cover these updates.

Enhancements to EIP-191 Message Handling:

• Serialized Signatures Support: Updated Eip191MessageBuilder to handle serialized signatures by integrating deserializeSignatures and modifying the fromBroadcastFormat method. [1] [2]
• Test Updates for EIP-191: Adjusted tests to validate serialized signatures, including changes to fixtures and methods for adding, replacing, and broadcasting signatures. [1] [2] [3] [4] [5] [6] [7]
• Fixture Adjustment: Updated fixtures to use structured signature objects, ensuring consistency with the new serialized signature format.

Introduction of CIP8 Standard for Cardano:

• CIP8 Message Implementation: Added Cip8Message class to handle CIP8 message creation, validation, and signing, leveraging Cardano serialization libraries and CBOR encoding.
• CIP8 Message Builder: Created Cip8MessageBuilder to construct and parse CIP8 messages, including support for serialized signatures.
• Utility Functions: Developed helper functions in utils.ts for constructing COSE objects and encoding/decoding operations.
• Message Builder Factory: Extended the factory to include support for CIP8 message builders.

Testing and Resources for CIP8:

• Test Resources: Added cip8Resources.ts to provide test data, including addresses, keys, and precomputed signatures for CIP8 messages.
• Module Index Updates: Updated index files to export new CIP8-related classes and utilities. [1] [2]

Miscellaneous Updates:

• Scope Addition: Updated .gitcommitscopes to include sdk-coin-ada, reflecting the new module for Cardano CIP8 support.

TICKET: COIN-4724