chore: Disallow implicit re-exports of imported values in Python modules

- Set Mypy option `no_implicit_reexport` to `True`.
- Fix errors reported by Mypy after the configuration change.

From https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-no-implicit-reexport:

> […] [do] not re-export unless the item is imported using from-as or is included in `__all__`.

Ref: https://app.shortcut.com/cordada/story/6589 [sc-6589]

mypy.ini

@@ -12,6 +12,7 @@ plugins =
 
 follow_imports = normal
 ignore_missing_imports = False
+no_implicit_reexport = True
 strict_optional = True
 disallow_untyped_defs = True
 check_untyped_defs = True

src/cl_sii/libs/crypto_utils.py

@@ -38,6 +38,11 @@
 
 """
 
+__all__ = [
+    'X509Cert',
+    '_X509CertOpenSsl',
+]
+
 import base64
 from typing import Union
 

src/cl_sii/libs/xml_utils.py

@@ -20,6 +20,11 @@
 
 """
 
+__all__ = [
+    'XmlElement',
+    'XmlElementTree',
+]
+
 import io
 import logging
 import os