Added Australian registration

[licon4812]

This pull request introduces a new feature to generate Australian vehicle registration plates with state-specific formats. It includes both the implementation of the feature and corresponding unit tests to ensure correctness. The most important changes are grouped into feature implementation and testing.

Feature Implementation:

• Added a new extension method AusCarRegistrationPlate in ExtensionsForAustraliaRegistrationPlate.cs to generate Australian vehicle registration plates based on the state, year, and date range. This method validates the state, determines the registration date, and applies state-specific formatting rules.
• Defined PlateFormatRule and StatePlateRules to encapsulate the logic for state-specific plate formats based on year ranges, including support for custom generation logic.
• Implemented helper methods such as GenerateRegistrationDate, GenerateRegistrationPlate, and GeneratePlateFromFormat to handle random date generation, format selection, and plate string construction.

Testing:

• Added a new test class AustraliaExtensionTests in AustraliaExtensionTests.cs containing unit tests to verify the correctness of the AusCarRegistrationPlate method for various states and year ranges.
• Included a parameterized test Generates_Correct_Plate_Format_For_State_And_Year to validate that the generated plate matches the expected format for a given state and year.
• Added a test Generates_Correct_Plate_Format_For_Random_State to ensure that the method works correctly when no specific state is provided, generating a valid plate for a random state.