feat(webdav): implement Getter interface

[ZRHann]

Description / 描述

为webdav driver实现Getter interface。这可以让原本访问a/b/c时的a，a/b，a/b/c三次请求，减少成一次a/b/c请求，优化性能。

Implement the Getter interface for the WebDAV driver. This optimizes performance by reducing the three separate requests typically required to access a/b/c (for a, a/b, and a/b/c) into a single request.

Motivation and Context / 背景

Closes #XXXX

Relates to #XXXX

How Has This Been Tested? / 测试

打log确定使用了op.Get。

Checklist / 检查清单

• I have read the CONTRIBUTING document.
  我已阅读 CONTRIBUTING 文档。
• I have formatted my code with go fmt or prettier.
  我已使用 go fmt 或 prettier 格式化提交的代码。
• I have added appropriate labels to this PR (or mentioned needed labels in the description if lacking permissions).
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• I have requested review from relevant code authors using the "Request review" feature when applicable.
  我已在适当情况下使用"Request review"功能请求相关代码作者进行审查。
• I have updated the repository accordingly (If it’s needed).
  我已相应更新了相关仓库（若适用）。
  • OpenList-Frontend #XXXX
  • OpenList-Docs #XXXX