Generate a lazy sub-service accessor tree

[OmarAlJarrah]

Problem

A deep service tree shouldn't instantiate everything eagerly or duplicate raw/cooked impls.

Proposed change

Generate by lazy sub-service accessors; the root reuses the nested raw-response impl to halve the generated type count. Note by lazy vs a memoized supplier for any future Java target.

Prior art: openai-java's client impl (OpenAIClientImpl.kt).

Acceptance

• Lazy sub-service accessors
• Raw impl reused

Dependencies

• Related Generate two-tier raw/cooked service methods #55 — service-method codegen shape

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Priority: medium · Effort: small