common : add missing <fstream> include in common.h

[zhangrunda]

Overview

common/common.h declares fs_open_ifstream() which returns std::ifstream, but the header does not #include <fstream>.
The type was previously available only transitively through other includes.

On stricter toolchains (e.g. GCC trunk on aarch64/Graviton4) that transitive include is not present, so compilation fails with:error: 'ifstream' in namespace 'std' does not name a type

This adds the #include <fstream>, following the include-what-you-use principle.

Additional information

Fixes #25046

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES — used an AI assistant to help diagnose the root cause (transitive-include breakage) and review the fix. The one-line change and all decisions are my own, and I take responsibility for the submitted change.

[ggml-gh-bot]

Hi @zhangrunda, thanks for your contribution!

Per our contribution guidelines, the automated PR checker found the following issue(s) that need your attention:

• AI-generated content: This project does not accept PRs, descriptions or commit messages that are fully or predominantly AI-generated. If you have used AI to assist you in writing code, please make sure to disclose that explicitly.

---

Please note that maintainers reserve the right to make final decisions on PRs. If you believe there is a mistake, please comment below.