Add missing using keyword in snapshot-store DAO

[Arkatufus]

Memory leak caused by CancellationTokenSource has been observed in the snapshot store DAO.

Changes

Add missing using keyword in ByteArraySnapshotDao to make sure that all CancellationTokenSource are disposed properly.

Checklist

For significant changes, please ensure that the following have been completed (delete if not relevant):

• This change follows the Akka.NET API Compatibility Guidelines.
• I have reviewed my own pull request.

Latest dev Benchmarks

Benchmark was done by continuously creating new ReceivePersistentActor at the rate of 50 actors per second for 5 minutes. Memory snapshot were taken using Jetbrains DotMemory using API before and after the actor creation spam and were compared to check for memory leak.

This PR's Benchmarks

[Aaronontheweb]

LGTM