test: add unit tests for get_creator_info registration fields

[Seunfunmi-319509]

Summary

Closes #677

This PR adds unit tests for the get_creator_info view to verify that it
returns all creator fields correctly immediately after creator registration.

Changes

• Register a creator with a known display name and fee recipient
• Call get_creator_info
• Assert the returned display name matches the registered value
• Assert the returned fee recipient matches the registered address
• Assert total_supply is 0 after registration
• Assert holder_count is 0 after registration
• Assert registered_at is within 5 seconds of the test execution time

Validation

• Display name matches the registered value
• Fee recipient matches the registered address
• Total supply is 0 at registration
• Holder count is 0 at registration
• registered_at is within 5 seconds of the test execution time

Notes

This PR adds test coverage only and does not modify contract behavior.

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