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

Inizia dal punto di ingresso ZipFile.mkdir() e analizza come mode viene sanificato in external_attr, insieme al valore predefinito documentato. Confronta il comportamento con stat.S_IMODE e os.mkdir(); il lavoro è completo quando i bit del tipo di file sono esclusi e il valore predefinito viene mostrato come 0o777, verificando al contempo il PR collegato gh-154509 per il lavoro già in corso.