Add additional GC related benchmark

Given this performance regression in Python 3.14, it would be nice if we had a benchmark which would have more clearly shown it before final release. I have a new GC specific benchmark but it doesn't do things that would show this regression.

We should consider adding a new benchmark. The key features would be:

• creating a bunch of net new container objects, in order to trigger many, potentially young generation, collections
• creating tuple objects that can be untracked by the GC, in order to avoid slowing down full collections

Ideally we prefer to avoid a micro or synthetic benchmark and instead find some kind of real application that shows this regression. E.g. near the 3.13 release, we found a GC regression shown by Sphinx building Python docs. Something like that would be good.

Read the linked Python 3.14 performance regression and the existing GC-specific benchmark in pull request 381 first. Investigate a real application benchmark, rather than a synthetic microbenchmark, that creates many new container objects and untrackable tuples and exposes the regression; done means the benchmark clearly shows this behavior before release.