Add `create` for async-nats KV

[praveenperera]

Proposed change

The go library seems to have the Create function which succeeds to add a value for a key if it’s not set, or if the last operation was a delete.

However, the async-nats rust package seems to missing it.

// Create will add the key/value pair if it does not exist.
Create(key string, value []byte) (revision uint64, err error)

Use case

Leases / Distributed lock

Contribution

Yes

[Jarema]

Hey!

Thanks for creating the proposal.
Feel free to open a PR if you are willing to contribute :).

[praveenperera]

@Jarema I was looking at how its implemented in the go SDK. And the update with 0 revision makes sense.

But I'm not sure how to implement Create if it was deleted. In the go SDK it looks for ErrKeyDeleted error type, I wasn't able to find the equivalent error in Rust. Maybe I missed something?

pub enum EntryErrorKind {
    InvalidKey,
    TimedOut,
    Other,
}

Should I maybe use store.entry instead of store.get and make sure operation is Delete or Purge? That should probably work, I'll see if I can get a PR going soon.

[praveenperera]

@Jarema made a PR: #1206