__repr__ after a transpose is slow

[devin-petersohn]

Describe the problem

Previously, transpose was extremely slow and copied the entire dataset. Now we store some metadata and do the transpose at the same time as another operation.

It is instant to do df.T, but when you repr(df.T) it will trigger the transpose. We need to debug why it takes so long on the repr.

Source code / logs

> %time x = df.T
> %time repr(x)