Add AtomicCounter class to threading module

[haim0n]

• Implemented AtomicCounter class for thread-safe increment and decrement operations.
• Ensured thread safety using a Lock.

[ghost]

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[ZeroIntensity]

I think this needs to get discussed on DPO first. I'm not convinced that we need this.

[tomasr8]

Related issue: #124366

[ZeroIntensity]

That looks promising. I think there's more to this, though, and we should still probably go to DPO (but maybe an issue is fine).

A number of things that should still get discussed:

• What should we call these methods? (inc and dec are definitely subject to bikeshedding.)
• We should take a look at prior work in cereggii, which tests these kinds of things on PyPI.
• Do we want a C accelerator in the _thread module?
• On top of that, there was some inclination in that issue to add things like this to the C API.

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