fix: Ensure series are contiguous prior to transpose

[mcrumiller]

Resolves #14524.

This changes the signature of transpose from &self to &mut self because it now rechunks...is this considered a breaking change?

[ritchie46]

You can make it a mutable method and call:

*self = self.as_single_chunk_par();

[mcrumiller]

You can make it a mutable method and call:

*self = self.as_single_chunk_par();

Thanks @ritchie46 -- although then you can't call transpose on a dataframe unless it's declared mutable, and that doesn't seem like a good idea.

[ritchie46]

We do this on more places.