fix(python): expose inline types to downstream checkers (#3817)

## Summary

- publish the PEP 561 `py.typed` marker so downstream type checkers
consume the inline public annotations
- add a Pyright contract test that distinguishes synchronous `connect`
from awaited `connect_async`
- verify the marker is present in the installed package

## Root cause

The public Python module already annotated `lancedb.connect` as
synchronous and `lancedb.connect_async` as asynchronous. The private
native `_lancedb.connect` stub is intentionally awaitable because it
backs `connect_async`. However, the distribution did not include a PEP
561 marker, so downstream tools such as mypy could ignore the public
inline annotations and expose misleading or incomplete type information.

## Validation

- `python/.venv/bin/ruff format --check python/python/tests/test_db.py
python/python/type_tests/connect.py`
- `python/.venv/bin/ruff check .`
- `cd python && .venv/bin/pytest
python/tests/test_db.py::test_package_includes_pep_561_marker -q`
- `cd python && .venv/bin/pyright --pythonpath .venv/bin/python`
- downstream mypy contract check for both public connection functions

Fixes #2159

<!-- lance-gatekeeper-fix:v1 agent=b07901451487187fc03f61890d3aa6bb
generation=1 -->

Co-authored-by: lancedb-gatefixer[bot] <313497061+lancedb-gatefixer[bot]@users.noreply.github.com>

python/pyproject.toml

@@ -140,6 +140,7 @@ include = [
     "python/lancedb/remote/errors.py",
     "python/lancedb/embeddings/__init__.py",
     "python/lancedb/_lancedb.pyi",
+    "python/type_tests/connect.py",
 ]
 exclude = ["python/tests/"]
 pythonVersion = "3.13"