fix(render): preserve 120 fps pacing headroom

[qiin2333]

改了啥呀

• 把定时呈现的绝对提交余量固定为 2 ms，给 120 Hz 的 RenderService latch 留出稳定空间
• future lead 从半帧放宽到一帧，并加入 1 us PTS 量化容差
• 新增 120 FPS 双帧 burst 测试，保证两帧继续按 PTS 间隔送显；真正超过预算时才 catch-up

为啥要改

PR63 的半帧预算在 120 FPS 下只有约 5.21 ms。解码器只要同批吐出两帧，第二帧就会被这个小杂鱼阈值重新锚定到同一个 VSync，Surface 随后丢掉其中一帧，实际显示帧率因此跑不满。

修复后稳态 lead 是 2 ms，相比 PR63 只增加约 0.96 ms；一帧 future lead 只吸收瞬时 decoder burst，不恢复旧版固定一整帧排队。

验证

• c++ -std=c++17 -Wall -Wextra -Werror nativelib/src/main/cpp/presentation_scheduler.cpp nativelib/src/test/cpp/presentation_scheduler_test.cpp -I nativelib/src/main/cpp -o /tmp/moonlight_presentation_scheduler_test && /tmp/moonlight_presentation_scheduler_test
• npm run check
• node hvigorw.js assembleApp --mode project -p product=default -p buildMode=debug --no-daemon（DevEco SDK 6.1 / JBR 21，BUILD SUCCESSFUL）

Summary by CodeRabbit

• 改进

  • 优化高刷新率场景下的画面呈现调度，提升连续帧的时间一致性。
  • 改善成对帧突发到达时的处理，减少不必要的帧合并或跳过。
  • 调整未来帧调度窗口，使不同帧率和小数帧率下的延迟控制更加稳定。

• 测试

  • 新增并更新高刷新率及突发帧场景验证，确保追帧行为符合预期。

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

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Run ID: b815ed7a-391c-478a-b9c2-1fbc5ba5687e

📥 Commits

Reviewing files that changed from the base of the PR and between 7bd8695 and 486be08.

📒 Files selected for processing (3)

• nativelib/src/main/cpp/presentation_scheduler.cpp
• nativelib/src/main/cpp/presentation_scheduler.h
• nativelib/src/test/cpp/presentation_scheduler_test.cpp

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📝 Walkthrough

Walkthrough

调度器改用固定 2ms 提交前置时间，并将未来前置上限调整为初始前置时间加一帧间隔及量化余量。测试同步覆盖 120fps 突发帧事件序列和新的延迟预算边界。

Changes

演示调度器阈值调整

Layer / File(s)	Summary
调度阈值配置 nativelib/src/main/cpp/presentation_scheduler.cpp, nativelib/src/main/cpp/presentation_scheduler.h	使用固定 2ms 的提交与初始前置时间，并将最大未来前置时间改为初始前置时间加一帧间隔及 1µs 量化余量。
突发帧与延迟预算测试 nativelib/src/test/cpp/presentation_scheduler_test.cpp	新增 120fps 成对突发帧测试，验证 NONE 与 CATCH_UP 事件，并更新最大未来前置时间断言及测试入口。

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• AlkaidLab/moonlight-harmony#61：修改相同的 PtsPresentationScheduler 前置时间和未来前置阈值逻辑。
• AlkaidLab/moonlight-harmony#63：涉及相同的调度器前置时间、未来预算及 CATCH_UP/PHASE_SHIFT 测试预期。

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	标题简洁且准确概括了核心变更：修复渲染调度以保留 120 FPS 的节奏余量。
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

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• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/bound-host-paced-latency

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