Improper sanitization and documentation for `ZipFile.mkdir(mode)`

Bug report

Bug description:

When calling ZipFile.mkdir(), the user provided mode does not have the file format bits cleared, which may cause the created entry be recognized as an incorrect or unknown file format.

import io
import stat
import zipfile

with zipfile.ZipFile(io.BytesIO(), 'w') as zh:
    zh.mkdir('foo/', 0o107777)  # regular file
    zinfo = zh.getinfo('foo/')
    print(oct(stat.S_IFMT(zinfo.external_attr >> 16)))  # 0o140000 (socket file)

with zipfile.ZipFile(io.BytesIO(), 'w') as zh:
    zh.mkdir('foo/', 0o127777)  # symbolic link
    zinfo = zh.getinfo('foo/')
    print(oct(stat.S_IFMT(zinfo.external_attr >> 16)))  # 0o160000 (unknown)

Additionally, the current source code and doc for ZipFile.mkdir()'s default mode value are 511, which is identical to 0o777 but less intuitive.

Suggestion

Instead of the current sanitization:

zinfo.external_attr = ((0o40000 | mode) & 0xFFFF) << 16

we should probably sanitize the provided mode as what stat.S_IMODE does, i.e.:

zinfo.external_attr = (0o40000 | (mode & 0o7777)) << 16

We should probably also revise the source code and doc for ZipFile.mkdir()'s default mode value to 0o777, to be consistent with os.mkdir() and more intuitive.

CPython versions tested on:

3.14

Operating systems tested on:

No response

Linked PRs

• gh-154509

从 ZipFile.mkdir() 入口点开始，检查 mode 如何被清理为 external_attr，以及文档中记录的默认值。将其行为与 stat.S_IMODE 和 os.mkdir() 进行比较；完成标准是排除文件类型位，并将默认值显示为 0o777，同时检查已关联的 PR gh-154509，了解已经在进行的工作。