chore(langchain): disable pyright missing-import diagnostic in the optional test

LangChain is an optional integration and is not installed in the CI lint
environment (`rye sync --all-features` does not pull it in), so pyright cannot
resolve `langchain_core.*` imports in the test and fails with reportMissingImports.
Disable that diagnostic for this test module; the runtime is already guarded by
`pytest.importorskip("langchain_core")`.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: viniciusdsmello

tests/lib/integrations/test_langchain_callback.py

@@ -14,11 +14,13 @@
    assistant message.
 """
 
-# The handler under test lives in ``src/openlayer/lib`` which is excluded from
-# pyright (see ``[tool.pyright] ignore`` in pyproject.toml), so its dynamic
-# LangChain-derived types surface here as ``Unknown`` under strict mode. Use
-# basic mode for this test, matching how the lib source itself is type-checked.
-# pyright: basic
+# The handler under test lives in ``src/openlayer/lib`` (excluded from pyright
+# via ``[tool.pyright] ignore``) and depends on LangChain, an OPTIONAL
+# integration that is not installed in the lint/type-check environment. So its
+# imports don't resolve there and its dynamic types surface as ``Unknown``. Use
+# basic mode and disable the missing-import diagnostic for this test module;
+# the runtime is guarded by ``pytest.importorskip`` below.
+# pyright: basic, reportMissingImports=false
 
 from __future__ import annotations