Add repeated upsizing tests

[spaskalev]

Issue #128 reported a potential problem with repeated up-sizing the allocator. Add tests for this in both the normal and embedded modes. Instead of running the check invariant function (which also works but is a lot more slower) use the fragmentation metric. The basis of reasoning here is that if the resize does not alter the allocated slots in any way then the fragmentation metric should not change either.

Also fixed some formatting nits while at it.

[spaskalev]

@janedoe-lab please take a look, using this approach might help you in your case.

[spaskalev]

The 32-bit failure is interesting, it looks like there really is a bug there.

[janedoe-lab]

So I found some bugs in my codebase. But it was quite a massive overhaul. I can't replicate the bug from #128 anymore, but can't quite pinpoint which change did it. So right now I am 99.99% sure it was fully due to bugs in my codebase.

[spaskalev]

Glad to hear it. I did spend a few hours and the difference between 64 and 32 bit were expected so the allocator seems to be working fine in this scenario (16MB growing to 512MB). I documented that allocations are expected to remain when calling resize.

Note - resize is not optimized at all and it is slow, especially for large arenas with small alignment. You may want to pre-allocate a larger chunk if memory permits.

[janedoe-lab]

Thank you so much for all the work. So far it is rock-solid!