This is useful if you rely on the `on_tool_end` callback to detect which
tool has finished in a multi agents scenario.
For example, I'm working on a project where I consume the `on_tool_end`
event where the event could be emitted by many agents or tools. Right
now the only way to know which tool has finished would be set a marker
on the `on_tool_start` and catch it on `on_tool_end`.
I didn't want to break the signature of the function, but what would
have been cleaner would be to pass the same details as in
`on_tool_start`
Co-authored-by: blob42 <spike@w530>
33ebb05251