`Tool.to_code_prompt()` method does not extract `Returns: ...` from the function docstring

Example:

```python
@tool
def get_temperature(city: str) -> float:
"""
get the temperature of any city in the world

Args:
city: the city name

Returns:
float: temperature in Celsius
```
return 19.2

print(get_temperature.to_code_prompt()) # this call does not print 'Returns:\n float: temperature in Celsius'
```

Start at the Tool.to_code_prompt() entry point and reproduce the get_temperature example from the issue. Trace how the function docstring's Args section is extracted, then verify that the Returns section is included with its float description. Done means the printed prompt contains “Returns:\n float: temperature in Celsius”.

Written by the indexing model from the issue text.