Generate two-tier raw/cooked service methods

[OmarAlJarrah]

Problem

Callers sometimes need headers/status without paying for deserialization.

Proposed change

Generate each operation in two tiers — a cooked method returning the parsed body, and a raw method returning a lazy ParsedResponse<T> whose parse() consumes/closes the body. Compose error-mapping + deserialization as Response -> X handlers at the generated-service layer (not as HTTP-pipeline stages — the pipeline stays transport-pure and keeps returning a raw Response). Rely on Closeable + use {} + KDoc; don't pull in a @MustBeClosed lint annotation.

Prior art: openai-java's withRawResponse() services (ModelServiceImpl.kt).

Acceptance

• Raw + cooked tiers generated
• Error-mapping composed at the service layer
• Test

Builds on the ResponseHandler seam.

Dependencies

• Blocked by Add a ResponseHandler<T> seam with lazy parse-once ParsedResponse<T> #36 — ResponseHandler / ParsedResponse seam
• Blocked by Define a minimal OperationParams SPI feeding the context chain #57 — OperationParams SPI
• Related Unify the two pagination stacks into one #30, Collapse HttpResponseException into HttpException and hoist a Retryable interface #37 — pre-codegen contracts to settle first
• Related Generate a curated operation overload set, not the full cross-product #58, Generate a lazy sub-service accessor tree #59 — service-method shape

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Priority: high · Effort: medium