'Compression' is py type 'Optional[int]' [1]. Before this patch only 'int' was
supported. Now NEO/go also understands 'Compression' with value 'Nil'.

Without this patch, NEO/go client tests fail with

```
have: neos://127.0.0.1:19847,127.0.0.1:28658/1: load 7fffffffffffffff:0000000000000006: 127.0.0.1:39230 - 127.0.0.1:46143 .291: decode: decode: M: AnswerObject.Compression: msgp: attempted to decode type "nil" with method for "uint"
```

[1] See https://lab.nexedi.com/nexedi/neoppod/-/blob/e3cd5c5bf/neo/tests/protocol#L21
    The fourth argument is 'compression':
    https://lab.nexedi.com/nexedi/neoppod/-/blob/e3cd5c5bf/neo/storage/handlers/client.py#L77-78