[Bug Fix] Fixed import/recognition issues with postprocess-related modules when used as packages, preventing abnormal behavior caused by missing package initialization files.

[GaoHuaZhang]

PR Type / PR类型

• Feature（功能新增）
• Bugfix（Bug 修复）
• Docs（文档更新）
• CI/CD（持续集成/持续部署）
• Refactor（代码重构）
• Perf（性能优化）
• Dependency（依赖项更新）
• Test-Cases（测试用例更新）
• Other（其他）

Related Issue | 关联 Issue
Relates to #(issue ID / issue 编号)

🔍 Motivation / 变更动机

📝 Modification / 修改内容

• 新增 ais_bench/benchmark/utils/postprocess/__init__.py，确保 postprocess 目录被 Python 识别为包，从而修复相关导入问题。

📐 Associated Test Results / 关联测试结果

• 本地自测通过（请补充命令/日志/CI 链接）

✅ Checklist / 检查列表

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues. / 使用预提交或其他 linting 工具来修复潜在的 lint 问题。
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests. / 修复的 Bug 已完全由单元测试覆盖，导致 Bug 的情况应在单元测试中添加。
• The modification is covered by complete unit tests. If not, please add more unit tests to ensure the correctness. / 此拉取请求中的修改已完全由单元测试覆盖。如果不是，请添加更多单元测试以确保正确性。
• All relevant documentation (API docs, docstrings, example tutorials) has been updated to reflect these changes. / 所有相关文档（API 文档、文档字符串、示例教程）已更新以反映这些更改。

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects. / 如果此拉取请求对下游或其他相关项目有潜在影响，应在那些项目中测试此 PR。
• CLA has been signed and all committers have signed the CLA in this PR. / CLA 已签署，且本 PR 中的所有提交者均已签署 CLA。

[gemini-code-assist]

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