Update Type Hint for energy_correction

[ShuaishuaiYuan]

Adapted from the Pymatgen PR template.

Summary

Fix the type hint, it can either be a list of float or a single float. so I change it to a union.

Additional dependencies introduced (if any)

N/A

TODO (if any)

N/A

Checklist

N/A

[anjohan]

Thank you for the contribution, and for testing out the LMPOTF functionality!

Note that you're the first (known) external user of LMPOTF, please let us know if there are any issues with the tutorial, installation or running the code.

[ShuaishuaiYuan]

I enjoyed learning about this. so far so good. I am able to deploy this and run jobs in our clusters. the tutorials have been very helpful so far. Thank you very much! I am happy to continue point out things that I notice later.