Use an AtomicUint for tracking logging verbosity

[reem]

This is safer than using a regular uint, as it eliminates the chance of undefined data races by reading/writing to the verbosity concurrently.

Since we don't care too much about the precise ordering of load/store instructions here, we can use the Relaxed ordering but still get atomic operations.

[martinraison]

Nice! Thanks a lot for catching this :)

[reem]

@martinraison Absolutely, glad I could contribute!