feat: aiken-based bet-ref example

[euonymos]

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Remember to follow our Contributing Guide before submitting your pull request.

Summary

This PR shows the use of an Aiken-based contract for bet-ref example.

Type of Change

Please mark the relevant option(s) for your pull request:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring (improving code quality without changing its behavior)
• Documentation update (adding or updating documentation related to the project)

Checklist

Please ensure that your pull request meets the following criteria:

• I have read the Contributing Guide
• My code follows the project's coding style and best practices
• My code is appropriately commented and includes relevant documentation
• I have added tests to cover my changes
• All new and existing tests pass
• I have updated the documentation, if necessary

Testing

To run unified tests with Aiken-based contract use the following command:

export AIKEN_BET_REF=1; cabal run atlas-unified-tests