refactor(protected-phrases): extract config and text normalization helpers

python/ebook_search/protected_phrases/config/bad_ends.toml

@@ -0,0 +1,31 @@
+tokens = [
+  "a",
+  "an",
+  "and",
+  "any",
+  "as",
+  "at",
+  "be",
+  "because",
+  "but",
+  "by",
+  "can",
+  "could",
+  "do",
+  "for",
+  "from",
+  "have",
+  "if",
+  "of",
+  "or",
+  "some",
+  "than",
+  "the",
+  "these",
+  "this",
+  "to",
+  "will",
+  "with",
+  "would",
+  "did",
+]