Simplify lambda function in api.py for better readability

[coderabbitai]

As requested by @kirk0830, there is an opportunity to simplify the lambda function inside the list comprehension in . For more details, please refer to PR #93 and this comment.

[kirk0830]

after a refactor, the orbital generation code now supports both scipy.bfgs and various torch optimizer now, all optimizers sharing the same interface. the file api.py now only stores some util functions, so this issue is not valid anymore

[kirk0830]

@dyzheng could you check if you can close this issue?