Evaluate: A struct version of allocator

https://internals.rust-lang.org/t/why-bring-your-own-allocator-apis-are-not-more-popular-in-rust/14494/3?u=heroickatora

It seemed interesting to me because this has the distinct advantage of not necessitating a type parameter, which was also a 'revelation' when dealing with forward compatible ways to design markers for a type being transmutable from bytes (compare [my blog post on the topic](https://www.hardmo.de/article/2021-03-14-zst-proof-types.md#zsts-as-marker-trait-replacements)). This comes at the cost of extra layout size of all containers containing such an allocator.

Read the linked Rust internals forum post and the blog post about ZST marker traits. Examine the current allocator API in the static-alloc crate to understand the type parameter design. Look for container definitions to assess layout implications. The goal is to propose a struct-based allocator design that avoids type parameters but increases size.

Written by the indexing model from the issue text.