Python: .NET: skip agent-hooks output buffering when no interceptor enforces the output points

Follow-up from #7564 (thread with @westey-m: https://github.com/microsoft/agent-framework/pull/7564#discussion_r3802992779). Buffering exists for the output deny, so hook-type detection cannot waive it — but when NO registered interceptor evaluates output/post_model_call at all, pass-through streaming is legitimate under the contract's capability subsetting (AGENT-HOOKS-0.1 §3.2).

Proposed shape: an optional declared enforced-point set on the factory options (interceptors are opaque, so the caller declares; ACS-style manifests already carry exactly this), enabling a factory-time fast path that skips gate construction entirely. Open design questions captured from the review thread: per-factory vs per-run declaration; how records self-describe skipped points for auditors; whether the declaration belongs in the ResponsibleAI.AgentHooks emitter rather than this integration; symmetry with the Python feature (#7515 shipped zero-exposure-only the same way).