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

Comienza en el punto de entrada ZipFile.mkdir() e inspecciona cómo se sanea mode en external_attr, junto con el valor predeterminado documentado. Compara el comportamiento con stat.S_IMODE y os.mkdir(); se considera terminado cuando se excluyen los bits de tipo de archivo y el valor predeterminado se muestra como 0o777, comprobando al mismo tiempo el PR vinculado gh-154509 para ver el trabajo que ya está en curso.