[cleanup](iwyu) Remove unnecessary #include <vector> from 26 files

[shuke987]

Summary

• Remove unnecessary #include <vector> from 26 BE source files
• These files do not directly use std::vector
• The header is transitively available through other included headers

Identified by include-what-you-use (IWYU 0.24 / Clang 20) analysis.

Test plan

• Full BE incremental build passes with zero compilation errors
• CI pipeline

🤖 Generated with Claude Code

[hello-stephen]

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1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
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4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?