Investigate whether to repair or replace Wee Alloc

[Bargsteen]

Task description

We support a small allocator, wee_alloc, via a feature wee_alloc for our smart contracts.
wee_alloc is not maintained and it has some outstanding bugs related to memory leaks (rustwasm/wee_alloc#106).

We, therefore, want to investigate whether we should repair and replace wee_alloc.
The main goal is that we want an allocator that has a small code size and works well for most smart contracts. It can be a very simple allocator as smart contracts are always short-lived and usually quite simple (especially in terms of allocation patterns).