Add additional gc benchmark with pickletools (#437)

[pgdr]

Adds a benchmark reproducing the Python 3.14 garbage collector regression described in cpython/#140175.

This real-world case uses pickletools to demonstrate the performance issue.

Fixes #437.

[pgdr]

Python version	Running time (sec)
3.13	1.59
3.14	6.47
3.15a	1.55

These tests (and the PR) has N = 1'000'000. The downside is that running the benchmark (with Python 3.14) takes almost 10 minutes.

I could reduce the size of the instance to lower the overall running time, but it seems like the garbage collector bug doesn't "kick in" until we reach a certain size.

With N = 100'000, the slowdown is not as noticable:

Python version	Running time (ms)
3.13	162
3.14	197
3.15a	154

[pgdr]

@sergey-miryanov Thanks for the review. I have fixed all issues you pointed out.

[pgdr]

@sergey-miryanov Something strange happens here. Even though I use the context manager (tempfile.TemporaryDirectory), occasionally when I kill pyperformance, the directory remains not cleaned up.

I am not able to reproduce this behavior when not running with pyperf, though, so it might be related to the way pyperf sets up (parallel?) runners.

It sounds like a bug, but I can't tell where.

[sergey-miryanov]

Code looks good to me.

[sergey-miryanov]

@pgdr Thanks! It is up to pyperformance maintainers now.