Slicing DictOfSeries with multiple identical keys fails

Summary

The getitem operator returns an 'broken' dios when called with two identical keys.

Reproducible Example

import pandas as pd
import dios

d = dios.DictOfSeries(pd.DataFrame({"a": [1,2,3], "b": [2,3,4]}))

print(d[["a", "a"]])

What is the current bug behavior?

The operation yields an usable dios. That is not very precise, I know, but I couldn't find a better description.

What is the expected correct behavior?

A dios, with two duplicated columns.

Stacktrace

Click to expand

Paste any relevant stacktrace inside the ```

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)