Add test to reproduce issue in impl Stream for Entries causing filename truncation

[RazerM]

I tracked down this issue in astral-sh/uv#5450 (comment)

tokio-tar/src/archive.rs

Line 317 in 4ee3572

let val = ready_err!(Pin::new(&mut ef).poll_read_all(cx));

            if is_recognized_header && entry.header().entry_type().is_pax_local_extensions() {
                if self.pax_extensions.is_some() {
                    return Poll::Ready(Some(Err(other(
                        "two pax extensions entries describing \
                         the same member",
                    ))));
                }
                let mut ef = EntryFields::from(entry);
                let val = ready_err!(Pin::new(&mut ef).poll_read_all(cx));
                self.pax_extensions = Some(val);
                continue;
            }

if Pin::new(&mut ef).poll_read_all(cx) is Poll::Pending then ready_err! returns it, so the Pax extension is lost. The same would apply to a pending poll that occurs while a > longlink or longname is being prepared. When poll_next is called again the next entry header is parsed.

This PR demonstrates the issue by creating an AsyncRead impl which pends every second time it is polled.

Commenting out this line makes the test pass, because the reader doesn't enter a pending state in the "wrong" place.

It is probably also the cause of dignifiedquire#39

[azenla]

Interesting... I will try to poke at this during the weekend.