bug#73431: Add `setf` support for `stream.el` in ELPA

[Okamsn]

Stefan Monnier wrote:
>> Returning back to the bug report, that means that we should probably
>> just always handle setf'ing any element in a stream as an error, right?
> 
> That's my opinion, at least, yes.
> 
> 
>          Stefan
> 

Hello,

Related to my first message, is there a general way to make streams not 
confused with lists? I am going through the other features in `seq.el`, 
and I have seen that `seq-sort` is also broken for streams, because 
someone added a special implementation for lists. It looks like every 
time someone improves the situation for lists by adding a specialized 
method, that could break the feature for streams if a specialized method 
for streams isn't also added.

Is there a major downside to using `cl-defstruct` to define a stream?

Thank you.