Implement tokio::AsyncWrite for EntryStreamWriter

[untitaker]

When creating entries, we cannot use Tokio to write file contents. Fix
that.

[Majored]

The expected usage currently would be to use async-compat, like so:

let mut writer = ZipFileWriter::with_tokio(Cursor::new(Vec::new()));
let entry = ZipEntryBuilder::new("test.txt".into(), Compression::Deflate);
let writer = writer.write_entry_stream(entry.build()).await.unwrap().compat_write();

I know this isn't ideal, so I'm very much open to ideas of making the compatibility layer between the base implementation and tokio better. Will have a think about if we want to do it this way.

[untitaker]

well, the other option i see is to make the writer generic over the inner writer, and expose a type alias like type TokioEntryStreamWriter = EntryStreamWriter<Compat<???>>. but to be honest i find all of that very confusing because now you have additional generics and type aliases as part of the public documentation. tbh i wish that even in the case of ZipFileWriter it was hidden.