Selection type for offer selection. When Auto, the SDK will automatically select the best offer. When None, no offer will be selected (use base plan/option only). When Specific, the SDK will use the exact offer ID provided.
Auto-select the best offer (e.g., longest free trial or cheapest)
Don't select any offer - use base plan/option only
Use a specific offer by ID
Returns the ID if this is a Specific selection, null otherwise
Converts to the Offer type used in ProductItem