[net][at] Reject overlong numeric hostnames

[wyf-777]

拉取/合并请求描述：(PR description)

为什么提交这份PR (why to submit this PR)

_gethostbyname_by_device() copied numeric-looking hostnames into a 16-byte
stack buffer with strncpy(ipstr, name, strlen(name)). A 16-byte input removed
the terminator, while a 17-byte or longer input wrote beyond the buffer before
inet_aton() could reject it.

This path is reachable through the AT-backed resolver APIs, including
getaddrinfo() and gethostbyname*().

你的解决方案是什么 (what is your solution)

Cache the hostname length once, classify characters with the required unsigned
ctype input, and reject numeric-looking strings that cannot fit in ipstr.
For accepted strings, copy the validated length and add the terminator
explicitly. This keeps the existing AT/domain resolution behavior unchanged and
removes the unbounded stack write.

Fixes #11332

请提供验证的bsp和config (provide the config and bsp)

• BSP: Host-side validation using bsp/simulator headers and MSVC; no physical hardware required.
• .config: Compile-time coverage for RT_USING_AT, AT_USING_SOCKET, RT_USING_SAL, and RT_USING_NETDEV.
• action: GitHub Actions pending.

Testing

• PASS: MSVC /W4 /RTC1 /GS boundary harness using the numeric-host branch:
  15 bytes accepted, 16 and 17 bytes rejected.
• PASS: Direct compile of components/net/at/at_socket/at_socket.c with MSVC
  /W4; no warnings in the changed lines.
• PASS: MSVC /analyze; no diagnostics in the changed code.
• PASS: clang-format --dry-run --Werror -style=file -lines=1409:1457.
• PASS: git diff --check.

AI assistance: OpenAI Codex:GPT-5 assisted with investigation, implementation,
and local verification. The commit contains the matching Assisted-by trailer.

当前拉取/合并请求的状态 Intent for your PR

必须选择一项 Choose one (Mandatory):

• 本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
• 本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

• 已经仔细查看过代码改动的对比 Already check the difference between PR and old code
• 代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
• 没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已经被注释了的代码 All redundant code is removed and cleaned up
• 所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
• 对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
• 代码是高质量的 Code in this PR is of high quality
• 已经使用clang-format 源码格式化工具确保格式符合RT-Thread代码规范 This PR has been formatted with clang-format and complies with RT-Thread code specification
• 如果是新增bsp, 已经添加ci检查到.github/ALL_BSP_COMPILE.json 详细请参考链接BSP自查

[github-actions]

👋 感谢您对 RT-Thread 的贡献！Thank you for your contribution to RT-Thread!

为确保代码符合 RT-Thread 的编码规范，请在你的仓库中执行以下步骤运行代码格式化工作流（如果格式化CI运行失败）。
To ensure your code complies with RT-Thread's coding style, please run the code formatting workflow by following the steps below (If the formatting of CI fails to run).

---

🛠 操作步骤 | Steps

1. 前往 Actions 页面 | Go to the Actions page
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2. 点击 Run workflow | Click Run workflow

• Use workflow from 保持默认分支（通常为 master）
  Keep the default branch (usually master) in Use workflow from
• 在 branch 输入框填写 PR 分支 fix/at-resolver-numeric-host-overflow
  Enter PR branch fix/at-resolver-numeric-host-overflow in the branch field
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  Set files/directories to exclude (directories should end with "/")

3. 等待工作流完成 | Wait for the workflow to complete
   格式化后的代码将作为独立提交推送至你的分支。
   The formatting changes will be pushed to your branch as a separate commit.

完成后，提交将自动更新至 fix/at-resolver-numeric-host-overflow 分支，关联的 Pull Request 也会同步更新。
Once completed, commits will be pushed to the fix/at-resolver-numeric-host-overflow branch automatically, and the related Pull Request will be updated.

如有问题欢迎联系我们，再次感谢您的贡献！💐
If you have any questions, feel free to reach out. Thanks again for your contribution!

[github-actions]

📌 Code Review Assignment

🏷️ Tag: components

Reviewers: @Maihuanyi

Changed Files (Click to expand)

• components/net/at/at_socket/at_socket.c

🏷️ Tag: components_net_at

Reviewers: @Ryan-CW-Code @lizhen9880

Changed Files (Click to expand)

• components/net/at/at_socket/at_socket.c

---

📊 Current Review Status (Last Updated: 2026-09-07 12:13 CST)

• ⌛ @Maihuanyi Pending Review
• ⌛ @Ryan-CW-Code Pending Review
• ⌛ @lizhen9880 Pending Review

---

📝 Review Instructions

1. 维护者可以通过单击此处来刷新审查状态: 🔄 刷新状态
   Maintainers can refresh the review status by clicking here: 🔄 Refresh Status

2. 确认审核通过后评论 LGTM/lgtm
   Comment LGTM/lgtm after confirming approval

3. PR合并前需至少一位维护者确认
   PR must be confirmed by at least one maintainer before merging

ℹ️ 刷新CI状态操作需要具备仓库写入权限。
ℹ️ Refresh CI status operation requires repository Write permission.

[github-actions]

MemBrowse Memory Report

nuvoton-m487

• CODE: .text +16 B (+0.0%, 356,040 B / 524,288 B, total: 68% used)
  No memory changes detected for:
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