Fix react bug in 2.6.0 that cause tools without type hint to fail

[kalanyuz]

Problem

When using functions without type hints as tools in ReAct, the code would throw an error when trying to access arg_types[k] since arg_types would be empty. This made it impossible to use simple functions without type annotations as tools, even for basic operations.

Solution

Modified the tool argument parsing logic to:

1. First check if the tool has arg_types attribute
2. Then check if the specific argument key exists in arg_types
3. Only attempt type validation for arguments that have explicit type hints
4. Pass through arguments without type hints as-is

Added a test case test_tool_calling_without_typehint that demonstrates:

• A simple function foo(a, b) without type hints can be used as a tool
• Arguments are correctly passed through without type validation
• The tool executes successfully and returns expected results
• Previous tests, including the ones that uses pydantic args, does not break

[okhat]

Hey, great catch. Not sure when this regression happened. Will review soon.