Fix all test type errors and enable ty check on tests

- Fix test_basic.py: search() takes str not list
- Fix test_cli_prompt_template.py: add type: ignore for Mock assignments
- Fix test_prompt_template_persistence.py: match BaseSearcher.search signature
- Fix test_prompt_template_e2e.py: add type narrowing asserts after skip
- Fix test_readme_examples.py: use explicit kwargs instead of **model_args
- Fix metadata_filter.py: allow Optional[MetadataFilters]
- Update CI to run ty check on tests

tests/test_basic.py

@@ -91,7 +91,7 @@ def test_large_index():
         builder.build_index(index_path)
 
         searcher = LeannSearcher(index_path)
-        results = searcher.search(["word10 word20"], top_k=10)
-        assert len(results[0]) == 10
+        results = searcher.search("word10 word20", top_k=10)
+        assert len(results) == 10
         # Cleanup
         searcher.cleanup()