refactor: improve docstring parsing logic for Google style (#28730)

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- [x] **PR title**: "package: description"
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Description:  
Improved the `_parse_google_docstring` function in `langchain/core` to
support parsing multi-paragraph descriptions before the `Args:` section
while maintaining compliance with Google-style docstring guidelines.
This change ensures better handling of docstrings with detailed function
descriptions.

Issue:  
Fixes #28628

Dependencies:  
None.

Twitter handle:  
@isatyamks

---------

Co-authored-by: Erick Friis <erick@langchain.dev>
Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/core/langchain_core/utils/function_calling.py

@@ -615,7 +615,8 @@ def _parse_google_docstring(
                 arg for arg in args if arg not in ("run_manager", "callbacks", "return")
             }
             if filtered_annotations and (
-                len(docstring_blocks) < 2 or not docstring_blocks[1].startswith("Args:")
+                len(docstring_blocks) < 2
+                or not any(block.startswith("Args:") for block in docstring_blocks[1:])
             ):
                 msg = "Found invalid Google-Style docstring."
                 raise ValueError(msg)