fix missing await in async create_client

[realChesta]

What kind of change does this PR introduce?

The async create_client method is calling AsyncClient.create without awaiting it, leading to the return of a nested coroutine and falsifying the return type of create_client.

What is the current behavior?

Users of create_client need to use a double await to use this function, which doesn't correspond to the indicated return type.

What is the new behavior?

The method now correctly returns a coroutine that returns an AsyncClient on completion.

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