test(acp-next): add config option helpers

[nexxeln]

Summary

• add a pure acp-next config-option module for model, effort, and mode selectors
• handle slash-containing model ids, variant selection formatting, and ACP verifier categories
• cover the parsing and builder behavior with focused unit tests

Testing

• added unit tests for option construction, variant fallback, model parsing, and display formatting
• validated the new test file locally