Add a "bump allocator", a small and simple allocator for Wasm

[Bargsteen]

Purpose

This PR implements a new allocator for our smart contracts. It is simple and has a small code size. It uses more memory than a linked-list allocator such as wee_alloc, but for many contracts, this simplicity is sufficient and better.

Something I discovered while building this, is that the Rust compiler sets the initial number of pages in wasm modules to 17, which seems like quite a lot for smart contracts. Each page is 64KiB, so the initial memory is always ~1.1 MiB.

Closes https://github.com/Concordium/concordium-rust-smart-contracts/issues/379

TODO

• The templates do not compile since they use the published version of concordium-std, so we need to publish it first, then merge this PR. Business as usual, but still a bit annoying and error-prone.

Changes

• Implement a bump allocator
• Add a bump_alloc feature to concordium_std
• Add tests via the contract bump-alloc-tests
• Remove the wee_alloc feature (breaking)
• Change all contracts that use wee_alloc to use bump_alloc
• Update the concordium-std library documentation to reflect the new reality
• Bump MSRV to 1.72 in the testing lib to fix an issue with the indirect dependency ahash which requires MSRV 1.72.

Checklist

• [x] My code follows the style of this project.
• [x] The code compiles without warnings.
• [x] I have performed a self-review of the changes.
• [x] I have documented my code, in particular the intent of the hard-to-understand areas.
• [x] (If necessary) I have updated the CHANGELOG.

[abizjak]

@Bargsteen I suppose this is just waiting for us to release concordium-std/testing library before it can be merged?

[Bargsteen]

@Bargsteen I suppose this is just waiting for us to release concordium-std/testing library before it can be merged?

Yep :-)