fix(tools): prevent aria2c from hanging after downloads in dlmodels.sh

[lixingyuan0817]

Pull request checklist

• The PR has a proper title. Use semantic commit style (e.g. fix(tools): ...).
• Make sure this is ready to be merged into the relevant branch.
• Ensure you can run the code you submitted successfully:
  • tools/dlmodels.sh completes and exits after downloads finish (no indefinite wait)

PR type

• Bug fix

Description

本次 PR 修复 tools/dlmodels.sh 中 aria2c 下载完成后进程不退出、一直等待的问题。

影响范围：

• 仅影响模型下载脚本的下载流程与退出行为
• 不影响训练/推理逻辑与模型质量

验证方式：

• 本地运行 tools/dlmodels.sh，确认下载完成后脚本会正常结束并返回终端

Screenshot

before：

after：