perf: reduce client interceptor async layers

[SunSi12138]

来源

#195（Client interceptor non-async fast path）。

改动

• 合并 Client interceptor 链的 async 层：
  • 终端层：InvokeTerminalTrackedAsync 改为非 async 委托，status/error/elapsed 下沉到各 shape 的 InvokeTerminalAsync，通过共享 MarkTerminalSucceeded/Failed/Elapsed helper。
  • 外层：InvokeAsync 改为非 async 委托到 RunChainAsync，新增 RunTypedChainAsync<TResult> 供 unary/client-streaming 直接返回 typed result，避免 InvokeTypedAsync 的额外 async 层。

验证（242 CPU5，各 5 轮）

scenario	baseline B/op	candidate B/op	CPU
FixedDefault	950-951	951	25.97-28.00µs（无回退）
ClientInterceptor	1873-1875	1610-1613	28.25-30.65µs
ClientInterceptor2	—	1706-1708	—
ClientInterceptor8	—	2280-2283	—

• 1 层附加成本 -262 B（约 28.4%），达到 >=25% 门槛。
• feature-off 零回退；每加一层仍 +96 B。
• 928 单元测试 + 22 InterceptorIntegrationTests 通过。

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Delightful!

Reviewed commit: 7d8615037c

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[SunSi12138]

@codex review

补充了共享 outcome helper 重构（把 RunChainAsync / RunTypedChainAsync 的 status/error/elapsed 分类抽成 MarkChainSucceeded / MarkTerminalFailed / MarkTerminalElapsed，消除重复）。请评审最新提交。

注：CI 上一轮的 quick 集成测试失败是 GracefulStopShouldDrainOneHundredAcceptedCallsAndReleaseResources（非 interceptor 的 graceful-stop 用例），本地连跑 3 次均通过，属 flaky；已 rerun CI。

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Chef's kiss.

Reviewed commit: 0a98b1724a

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