Generate a per-endpoint SSE adapter mapping events to typed models

[OmarAlJarrah]

Problem

Streaming endpoints need to map raw SSE events to typed models with endpoint-specific conventions.

Proposed change

Generate a per-endpoint SSE adapter turning SseStream<ServerSentEvent> into Iterable<TModel>, with a configurable done-sentinel and error-envelope→exception mapping. Keep the sentinel/error conventions out of core (they're per-API). Decode each element lazily on consume via the Serde SPI.

Acceptance

• Per-endpoint SSE→model adapter
• Lazy per-element decode
• Test

Builds on the AutoCloseable SSE stream + ResponseHandler seam.

Dependencies

• Blocked by Make the SSE stream an AutoCloseable Iterable bound to response close #35 — AutoCloseable SSE stream
• Blocked by Add a ResponseHandler<T> seam with lazy parse-once ParsedResponse<T> #36 — ResponseHandler seam

---

Priority: medium · Effort: medium