Add ty type checker to CI and fix type errors (fixes bug from PR #157) (#192)

* Add ty type checker to CI and fix type errors

- Add ty (Astral's fast Python type checker) to GitHub CI workflow
- Fix type annotations across all RAG apps:
  - Update load_data return types from list[str] to list[dict[str, Any]]
  - Fix base_rag_example.py to properly handle dict format from create_text_chunks
- Fix type errors in leann-core:
  - chunking_utils.py: Add explicit type annotations
  - cli.py: Fix return type annotations for PDF extraction functions
  - interactive_utils.py: Fix readline import type handling
- Fix type errors in apps:
  - wechat_history.py: Fix return type annotations
  - document_rag.py, code_rag.py: Replace **kwargs with explicit arguments
- Add ty configuration to pyproject.toml

This resolves the bug introduced in PR #157 where create_text_chunks()
changed to return list[dict] but callers were not updated.

* Fix remaining ty type errors

- Fix slack_mcp_reader.py channel parameter can be None
- Fix embedding_compute.py ContextProp type issue
- Fix searcher_base.py method override signatures
- Fix chunking_utils.py chunk_text assignment
- Fix slack_rag.py and twitter_rag.py return types
- Fix email.py and image_rag.py method overrides

* Fix multimodal benchmark scripts type errors

- Fix undefined LeannRetriever -> LeannMultiVector
- Add proper type casts for HuggingFace Dataset iteration
- Cast task config values to correct types
- Add type annotations for dataset row dicts

* Enable ty check for multimodal scripts in CI

All type errors in multimodal scripts have been fixed, so we can now
include them in the CI type checking.

* 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

* Format code with ruff

* Format searcher_base.py

apps/multimodal/vision-based-pdf-multi-vector/multi-vector-leann-paper-example.py

@@ -18,10 +18,11 @@ _repo_root = Path(__file__).resolve().parents[3]
 _leann_core_src = _repo_root / "packages" / "leann-core" / "src"
 _leann_hnsw_pkg = _repo_root / "packages" / "leann-backend-hnsw"
 if str(_leann_core_src) not in sys.path:
-    sys.path.append(str(_leann_core_src))
+    sys.path.insert(0, str(_leann_core_src))
 if str(_leann_hnsw_pkg) not in sys.path:
-    sys.path.append(str(_leann_hnsw_pkg))
+    sys.path.insert(0, str(_leann_hnsw_pkg))
 
+from leann_multi_vector import LeannMultiVector
 
 import torch
 from colpali_engine.models import ColPali
@@ -93,9 +94,9 @@ for batch_doc in tqdm(dataloader):
 print(ds[0].shape)
 
 # %%
-# Build HNSW index via LeannRetriever primitives and run search
+# Build HNSW index via LeannMultiVector primitives and run search
 index_path = "./indexes/colpali.leann"
-retriever = LeannRetriever(index_path=index_path, dim=int(ds[0].shape[-1]))
+retriever = LeannMultiVector(index_path=index_path, dim=int(ds[0].shape[-1]))
 retriever.create_collection()
 filepaths = [os.path.join("./pages", name) for name in page_filenames]
 for i in range(len(filepaths)):