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

.github/workflows/build-reusable.yml

@@ -47,8 +47,8 @@ jobs:
 
       - name: Run ty type checker
         run: |
-          # Run ty on core packages and apps, excluding tests
-          ty check --exclude "tests/**" packages/leann-core/src apps
+          # Run ty on core packages, apps, and tests
+          ty check packages/leann-core/src apps tests
 
   build:
     needs: [lint, type-check]