Not able to use the Async (non-blocking) version of the KMS Client

### Problem:

Not able to use the SDK with the async (non-blocking) version of the KMS Client

### Solution:

A KmsMasterKeyProvider should be provided from the SDK that internally uses the KmsAsyncClient

Start by tracing the existing KmsMasterKeyProvider and how it constructs or uses the KMS client, then compare that path with the requested KmsAsyncClient. Define the async provider's supported behavior and integration boundaries before making changes. Done means the SDK exposes a usable non-blocking KMS master-key provider and verifies its behavior with appropriate tests.

Written by the indexing model from the issue text.