Result type for Planck.AI.evaluate/4.

A thin, name-only alias over ReqLLM.Response.t() — not a reshaped struct. response.object (the answers map, keyed by question name) and response.usage come through completely unchanged; evaluate/4 deliberately doesn't rebuild this value the way Planck.AI.Stream.from_req_llm/1 does for stream/3.

Exists purely so callers (in particular planck_agent, which never depends on req_llm directly) reference a Planck.AI-owned type name instead of reaching into req_llm's own ReqLLM.Response directly — the same abstraction boundary Planck.AI.Stream.t() already maintains for stream/3, at zero runtime cost since this is a pure type alias.