Test what an ideal scope pool size is

[dphfox]

In #312 (later implemented by #273) a scope pool was implemented, to facilitate reuse of empty allocations across objects and reduce the load on the memory allocator when processing many callbacks that may or may not require the use of a scope.

Right now up to 16 scopes can be saved at a time, but testing is required to verify what an optimal number looks like for a realistic program.

[dphfox]

It would also be good to do ablation to compare against a baseline implementation which does not reuse scopes in this manner.