feat: Enhance series metadata extraction from categories in OPDS feed

tests/test_calibre_opds.py

@@ -31,3 +31,33 @@ def test_calibre_opds_feed_exposes_series_metadata() -> None:
     feed_dict = feed_to_dict(feed)
     assert feed_dict["entries"][0]["series"] == "The Expanse"
     assert feed_dict["entries"][0]["series_index"] == 4.0
+
+
+def test_calibre_opds_feed_extracts_series_from_categories() -> None:
+    client = CalibreOPDSClient("http://example.com/catalog")
+    xml_payload = """<?xml version=\"1.0\" encoding=\"UTF-8\"?>
+    <feed xmlns=\"http://www.w3.org/2005/Atom\"
+          xmlns:dc=\"http://purl.org/dc/terms/\"
+          xmlns:calibre=\"http://calibre.kovidgoyal.net/2009/catalog\">
+      <id>catalog</id>
+      <title>Example Catalog</title>
+      <entry>
+        <id>book-2</id>
+        <title>Network Effect</title>
+        <category
+          scheme=\"http://calibre.kovidgoyal.net/2009/series\"
+          term=\"The Murderbot Diaries #5\"
+          label=\"The Murderbot Diaries [5]\" />
+        <link rel=\"http://opds-spec.org/acquisition\"
+              href=\"books/network-effect.epub\"
+              type=\"application/epub+zip\" />
+      </entry>
+    </feed>
+    """
+
+    feed = client._parse_feed(xml_payload, base_url="http://example.com/catalog")
+    assert feed.entries, "Expected at least one entry in parsed feed"
+    entry = feed.entries[0]
+
+    assert entry.series == "The Murderbot Diaries"
+    assert entry.series_index == 5.0