gp-opengraph(refactor[imports]): use namespace imports for stdlib modules

why: PR #22 code review flagged three ``from <stdlib> import <name>``
import statements that violate CLAUDE.md line 457:

    Use namespace imports for standard library modules:
    `import enum` instead of `from enum import Enum`
    Exception: `dataclasses` module may use
    `from dataclasses import dataclass, field` for cleaner
    decorator syntax

Every existing workspace package follows this — e.g. gp-sphinx's own
config.py uses ``import pathlib`` / ``import tomllib`` then
``pathlib.Path(...)`` / ``tomllib.loads(...)``.

what:
- packages/gp-opengraph/src/gp_opengraph/__init__.py:
  * ``from types import NoneType`` -> ``import types`` +
    ``types.NoneType`` at each call site (four occurrences inside
    ``frozenset({...})`` literals for add_config_value).
  * ``from urllib.parse import urljoin, urlparse, urlsplit, urlunsplit``
    -> ``import urllib.parse`` with each call qualified:
    ``urllib.parse.urljoin(...)``, ``urllib.parse.urlparse(...)``,
    ``urllib.parse.urlsplit(...)``, ``urllib.parse.urlunsplit(...)``.
- packages/gp-opengraph/src/gp_opengraph/_title.py:
  * ``from html.parser import HTMLParser`` -> ``import html.parser``;
    subclass declaration becomes ``class HTMLTextParser(html.parser.HTMLParser)``.
- packages/gp-opengraph/src/gp_opengraph/_meta.py:
  * Same HTMLParser rewrite as _title.py.

Left as-is (already compliant):
- ``from xml.etree import ElementTree`` in gp_sitemap — this imports a
  *submodule*, not a name, and is the canonical idiom (equivalent to
  ``import xml.etree.ElementTree as ElementTree``). CLAUDE.md's
  example targets ``from enum import Enum`` (name import), not
  submodule aliasing.
- ``from collections.abc import Set`` / ``Iterable`` inside
  ``TYPE_CHECKING`` blocks — gp_sphinx itself does this at
  config.py#L17, so the convention allows type-only imports this way.

No behavior change; purely an import refactor.

CI gate (all green before commit):
- uv run ruff check . --fix --show-fixes: clean
- uv run ruff format .: no changes
- uv run mypy: Success (176 source files)
- uv run py.test --reruns 0 -vvv: 1199 passed, 3 skipped
- just build-docs: build succeeded

Author: tony

packages/sphinx-gp-opengraph/src/sphinx_gp_opengraph/__init__.py

@@ -22,9 +22,9 @@
 import logging
 import os
 import pathlib
+import types
 import typing as t
-from types import NoneType
-from urllib.parse import urljoin, urlparse, urlsplit, urlunsplit
+import urllib.parse
 
 from docutils import nodes
 from sphinx.application import Sphinx
@@ -137,7 +137,7 @@ def get_tags(
 
     ogp_canonical_url = config.ogp_canonical_url or ogp_site_url
 
-    page_url = urljoin(
+    page_url = urllib.parse.urljoin(
         ogp_canonical_url,
         builder.get_target_uri(context["pagename"]),
     )
@@ -170,10 +170,10 @@ def get_tags(
 
     if image_url:
         if "og:image" not in fields:
-            image_url_parsed = urlparse(image_url)
+            image_url_parsed = urllib.parse.urlparse(image_url)
             if not image_url_parsed.scheme:
                 root = page_url if first_image else ogp_site_url
-                image_url = urljoin(root, image_url_parsed.path)
+                image_url = urllib.parse.urljoin(root, image_url_parsed.path)
             tags["og:image"] = image_url
 
         if isinstance(ogp_image_alt, str):
@@ -204,8 +204,10 @@ def _ambient_site_url() -> str:
     if not rtd_canonical_url:
         msg = "ReadTheDocs did not provide a valid canonical URL"
         raise RuntimeError(msg)
-    parsed = urlsplit(rtd_canonical_url)
-    return urlunsplit((parsed.scheme, parsed.netloc, parsed.path, "", ""))
+    parsed = urllib.parse.urlsplit(rtd_canonical_url)
+    return urllib.parse.urlunsplit(
+        (parsed.scheme, parsed.netloc, parsed.path, "", ""),
+    )
 
 
 def _resolve_site_name(config: Config) -> str | None:
@@ -300,13 +302,13 @@ def setup(app: Sphinx) -> dict[str, t.Any]:
         "ogp_image",
         None,
         "html",
-        types=frozenset({str, NoneType}),
+        types=frozenset({str, types.NoneType}),
     )
     app.add_config_value(
         "ogp_image_alt",
         None,
         "html",
-        types=frozenset({str, bool, NoneType}),
+        types=frozenset({str, bool, types.NoneType}),
     )
     app.add_config_value(
         "ogp_use_first_image",
@@ -319,14 +321,14 @@ def setup(app: Sphinx) -> dict[str, t.Any]:
         "ogp_site_name",
         None,
         "html",
-        types=frozenset({str, bool, NoneType}),
+        types=frozenset({str, bool, types.NoneType}),
     )
     # Accepted-but-ignored: warned about in _warn_if_social_cards_used.
     app.add_config_value(
         "ogp_social_cards",
         None,
         "html",
-        types=frozenset({dict, NoneType}),
+        types=frozenset({dict, types.NoneType}),
     )
     app.add_config_value(
         "ogp_custom_meta_tags",

packages/sphinx-gp-opengraph/src/sphinx_gp_opengraph/_meta.py

@@ -15,7 +15,7 @@
 
 from __future__ import annotations
 
-from html.parser import HTMLParser
+import html.parser
 
 
 def get_meta_description(meta_tags: str) -> str | bool | None:
@@ -40,7 +40,7 @@ def get_meta_description(meta_tags: str) -> str | bool | None:
     return htp.meta_description
 
 
-class HTMLTextParser(HTMLParser):
+class HTMLTextParser(html.parser.HTMLParser):
     """Flag the presence (and content) of a ``<meta name="description">``."""
 
     def __init__(self) -> None:

packages/sphinx-gp-opengraph/src/sphinx_gp_opengraph/_title.py

@@ -11,7 +11,7 @@
 
 from __future__ import annotations
 
-from html.parser import HTMLParser
+import html.parser
 
 
 def get_title(title: str) -> tuple[str, str]:
@@ -38,7 +38,7 @@ def get_title(title: str) -> tuple[str, str]:
     return htp.text, htp.text_outside_tags
 
 
-class HTMLTextParser(HTMLParser):
+class HTMLTextParser(html.parser.HTMLParser):
     """Track text-inside-tags vs text-outside-tags while parsing HTML."""
 
     def __init__(self) -> None: