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-similarity-map.py

@@ -5,7 +5,7 @@ import argparse
 import faulthandler
 import os
 import time
-from typing import Any, Optional
+from typing import Any, Optional, cast
 
 import numpy as np
 from PIL import Image
@@ -223,7 +223,7 @@ if need_to_build_index:
         # Use filenames as identifiers instead of full paths for cleaner metadata
         filepaths = [os.path.basename(fp) for fp in filepaths]
     elif USE_HF_DATASET:
-        from datasets import load_dataset, concatenate_datasets, DatasetDict
+        from datasets import Dataset, DatasetDict, concatenate_datasets, load_dataset
 
         # Determine which datasets to load
         if DATASET_NAMES is not None:
@@ -281,12 +281,12 @@ if need_to_build_index:
                 splits_to_load = DATASET_SPLITS
 
             # Load and concatenate multiple splits for this dataset
-            datasets_to_concat = []
+            datasets_to_concat: list[Dataset] = []
             for split in splits_to_load:
                 if split not in dataset_dict:
                     print(f"  Warning: Split '{split}' not found in dataset. Available splits: {list(dataset_dict.keys())}")
                     continue
-                split_dataset = dataset_dict[split]
+                split_dataset = cast(Dataset, dataset_dict[split])
                 print(f"  Loaded split '{split}': {len(split_dataset)} pages")
                 datasets_to_concat.append(split_dataset)