Refactor JWT Class into JWTDecoder and JWTSigner, Improve Type Safety and Test Coverage

[mosquito]

This pull request introduces significant architectural improvements to the JWT implementation, enhancing clarity, separation of concerns, and test robustness. The monolithic JWT class is split into two distinct classes: JWTDecoder and JWTSigner, each tailored for their specific responsibilities. Additionally, tests have been streamlined, parameterized, and modernized for better coverage and maintainability.

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Key Changes:

1. Refactor JWT Class

• Split into JWTDecoder and JWTSigner:
  • JWTDecoder: Handles JWT token decoding.
  • JWTSigner: Inherits from JWTDecoder, adds encoding functionality using a private key.
• Use @dataclass for Immutability and Cleaner Initialization:
  • Leverages dataclasses.field to manage internal fields securely.
• Improved Method Clarity:
  • Removed _date_to_timestamp method duplication.
  • Refactored logic into a reusable date_to_timestamp function.
• Added Overloaded Factory Method (JWT)
  • Dynamically returns either JWTDecoder or JWTSigner based on the provided key type.

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2. Test Suite Enhancements:

• Removed Unnecessary Mocks:
  • Direct argument passing replaces mock.patch usage.
• Parameterized Tests:
  • test_rsa_verify and test_rsa_verify_bad_key now use pytest.mark.parametrize for better coverage across different formats (jwk, pem, base64).
• Improved Exception Assertions:
  • More precise exception types are asserted (AttributeError instead of RuntimeError, TypeError instead of ValueError).

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3. Minor Fixes and Improvements:

• Cleaned up imports.
• Removed deprecated or redundant code blocks.
• Improved error messages for invalid key types in the factory function.

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Backward Compatibility:

• This refactor introduces breaking changes for users who relied on the previous JWT class structure.
• However, the new interface is cleaner, type-safe, and more explicit.

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Testing:

• All tests have been updated to match the new architecture.
• New edge cases have been added, particularly in key validation scenarios.
• CI Pipeline passes successfully.