Improve retrieval of binaryChecksum

[taylanisikdemir]

What changed? binaryChecksum gets initialized somewhere early on in worker's lifecycle and then read many times. It was protected by a sync.Mutex for both reads and writes. Typically sync.Once is used for such scenarios but there is a SetBinaryChecksum() function exposed so it wouldn't work here. Changing the implementation to avoid mutex locks for reads once binaryChecksum is initialized/set.

Why? This change might not have visible performance improvements but still better to use atomic instead of a mutex each time binaryChecksum is read.

How did you test it? make test

Potential risks N/A

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