Fix intermittent H264EncoderTools not found issue on Windows by waiting for devenv to complete.

[CodeJhF]

修复 Windows 平台上偶现的无法找到 H264EncoderTools 的问题。

问题原因：devenv.exe 默认异步启动，编译任务在后台进行时脚本已继续执行，导致复制编译产物时文件可能不存在。

修复方案：

1. 使用 Start-Process -Wait -PassThru 确保等待 devenv.exe 完成编译后再继续
2. 添加 H264EncoderTools.exe 存在性检查，若文件不存在则报错退出

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.13%. Comparing base (d836825) to head (52edfac).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3244      +/-   ##
==========================================
+ Coverage   77.04%   77.13%   +0.09%     
==========================================
  Files         413      415       +2     
  Lines       21922    22040     +118     
  Branches     6298     6307       +9     
==========================================
+ Hits        16890    17001     +111     
+ Misses       3821     3815       -6     
- Partials     1211     1224      +13     

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