[simple] updated annotation in load_tools.py (#3544)
- added a few missing annotation for complex local variables.
- auto formatted.
- I also went through all other files in agent directory. no seeing any
other missing piece. (there are several prompt strings not annotated,
but I think it’s trivial. Also adding annotation will make it harder to
read in terms of indents.) Anyway, I think this is the last PR in
agent/annotation.
