Core: google docstring parsing fix (#28404)

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- [ ] **PR title**: "core: google docstring parsing fix"


- [x] **PR message**:
- **Description:** Added a solution for invalid parsing of google
docstring such as:
    Args:
net_annual_income (float): The user's net annual income (in current year
dollars).
- **Issue:** Previous code would return arg = "net_annual_income
(float)" which would cause exception in
_validate_docstring_args_against_annotations
    - **Dependencies:** None

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, ccurme, vbarda, hwchase17.

Co-authored-by: Erick Friis <erick@langchain.dev>

libs/core/langchain_core/utils/function_calling.py

@@ -646,9 +646,13 @@ def _parse_google_docstring(
         for line in args_block.split("\n")[1:]:
             if ":" in line:
                 arg, desc = line.split(":", maxsplit=1)
-                arg_descriptions[arg.strip()] = desc.strip()
+                arg = arg.strip()
+                arg_name, _, _annotations = arg.partition(" ")
+                if _annotations.startswith("(") and _annotations.endswith(")"):
+                    arg = arg_name
+                arg_descriptions[arg] = desc.strip()
             elif arg:
-                arg_descriptions[arg.strip()] += " " + line.strip()
+                arg_descriptions[arg] += " " + line.strip()
     return description, arg_descriptions