client: Add async to anchor-client

[Aursen]

No description provided.

[vercel]

@Aursen is attempting to deploy a commit to the coral-xyz Team on Vercel.

A member of the Team first needs to authorize it.

[acheroncrypto]

I made the subscription method the same as the blocking version(no need event handler) and subscriptions only return an unsubscribe function instead of a subscription id(since this is also what solana_client returns). Let me know what you think!

Before:

let mut event_handler = program.create_event_handler().await?;
let event_id = event_handler.subscribe(...)?;
event_handler.unsubscribe(event_id).await;

After:

let event = program.on(...).await?;
event.unsubscribe().await;

One issue is that there is still too much duplicate code. What do you think we can do about it?

[Aursen]

For the duplication, I need to think a bit

[acheroncrypto]

Thank you for taking the time to reduce the duplication. I think it looks much better overall, and will be easier to maintain.

Let me know if there are any issues with the other comment.

[acheroncrypto]

Thank you, looks great!

[acamill]

Any example of rust code using an async client?

[acheroncrypto]

Any example of rust code using an async client?

Here is an example https://github.com/coral-xyz/anchor/blob/master/client/example/src/nonblocking.rs

[acamill]

Thanks!