Separate unfold resources from unfolder construction #946

Summary

Redesign the unfold registration API so resource dependencies belong to the unfold operation, rather than being passed through input_family(...) alongside product selectors for constructing the unfolder.

Current behavior

input_family(...) product selectors configure the unfolder constructor, while trailing resource<T> arguments are applied to the unfold operation. This mixes two distinct concerns in one clause and makes the API semantics confusing. The unfolder constructor is not allowed to receive resources.

Desired behavior

Provide a distinct, explicit way to declare resources used by the unfold operation. Keep input_family(...) focused on matching products to the unfolder constructor, and ensure its constructor parameters do not include resources.

Acceptance criteria

• The API expresses unfold-operation resource dependencies separately from unfolder-constructor inputs.
• Product selectors in input_family(...) continue to correspond only to unfolder constructor parameters.
• Unfolder constructors cannot receive resources.
• Resources are provided to the unfold operation with the existing unlimited/serialized resource semantics and concurrency guarantees.
• Tests cover constructor inputs and unfold-operation resource access independently.