[BUG] get metadata

### Is there an existing issue for this?

- [X] I have searched the existing issues

### What version of `workers-rs` are you using?

0.0.11

### Describe the bug

let (value, metadata) = kv.get(&idid).bytes_with_metadata::>().await?;

how get **metadata**?

### Steps To Reproduce

worker = "0.0.11"
wrangler kv:key put --binding=templates $filenamenopath --preview false --path $file --metadata '{"Metadata":"Json"}'

let (value, metadata) = kv.get(&idid).bytes_with_metadata::>().await?;
console_log!("{:?}", metadata.unwrap_or_default());

"KvError::Serialization: invalid type: map, expected a sequence at line 1 column 0"