Allocation mechanisms improvements

[m4drat]

• [ ] ❓ Change allocation logic (firstly reuse all available space in free list, and only then allocate new arena). This one is under a question mark, because with that implementation we are losing benefits of simple bump allocator. But the idea in general is that we should use free-list more.
• [ ] ✔ Try to reuse the most appropriate chunks from chunk treap first (GetFirstGreaterOrEqualToChunk -> upper_bound). To do so it is a great idea to implement #39 (just to use std::lower_bound)
• [x] ✔ Before doing anything, complete #29 and collect some base measurements.