Replace remaining os.path usage with pathlib across codebase

Modernize all remaining os.path operations to use pathlib.Path for
consistency:
- sphinx_exercise/__init__.py: Use Path for package/locale directory
- sphinx_exercise/post_transforms.py: Use Path.with_suffix('')
- sphinx_exercise/translations/_convert.py: Use Path.resolve()

This completes the migration to pathlib throughout the codebase,
keeping only os.sep in tests where it's appropriate for path
separator normalization.

Author: mmcky

sphinx_exercise/__init__.py

@@ -9,7 +9,6 @@
 
 __version__ = "1.0.1"
 
-import os
 from pathlib import Path
 from typing import Any, Dict, Set, Union, cast
 from sphinx.config import Config
@@ -215,9 +214,9 @@ def setup(app: Sphinx) -> Dict[str, Any]:
     app.add_css_file("exercise.css")
 
     # add translations
-    package_dir = os.path.abspath(os.path.dirname(__file__))
-    locale_dir = os.path.join(package_dir, "translations", "locales")
-    app.add_message_catalog(MESSAGE_CATALOG_NAME, locale_dir)
+    package_dir = Path(__file__).parent.resolve()
+    locale_dir = package_dir / "translations" / "locales"
+    app.add_message_catalog(MESSAGE_CATALOG_NAME, str(locale_dir))
 
     return {
         "version": "builtin",

sphinx_exercise/post_transforms.py

@@ -1,4 +1,5 @@
-import os
+from pathlib import Path
+
 import sphinx.addnodes as sphinx_nodes
 from sphinx.transforms.post_transforms import SphinxPostTransform
 from sphinx.util import logging
@@ -196,7 +197,7 @@ def run(self):
                     except AttributeError:
                         docname = self.env.docname  # for builder such as JupyterBuilder that don't support current_docname
                 docpath = self.env.doc2path(docname)
-                path = os.path.splitext(docpath)[0]
+                path = str(Path(docpath).with_suffix(""))
                 msg = f"undefined label: {target_label}"
                 logger.warning(msg, location=path, color="red")
                 return

sphinx_exercise/translations/_convert.py

@@ -1,5 +1,4 @@
 import json
-import os
 from pathlib import Path
 import subprocess
 
@@ -54,9 +53,9 @@ def convert_json(folder=None):
         subprocess.check_call(
             [
                 "msgfmt",
-                os.path.abspath(path),
+                str(path.resolve()),
                 "-o",
-                os.path.abspath(path.parent / f"{MESSAGE_CATALOG_NAME}.mo"),
+                str((path.parent / f"{MESSAGE_CATALOG_NAME}.mo").resolve()),
             ]
         )