build(deps): remove wee_alloc

[afonsobarracha]

Description

wee_alloc is no longer maintained and has memory leaks, so I am removing that feature. We will now default to the rust standard allocator, to insure this is always the best version it can be we will use a recent version of rust.

To ensure the maximum possible performance from the standard allocator, the rust edition will be updated to 2021, and the rustup version will be set at 1.72.x, currently the newest version of rust.

• Tests for the changes have been added (for bug fixes / features)
• The commit message(s) follow conventional commits
• Documentation has been added / updated (for bug fixes / features)
• Changes follow the contributing document.

Motivation and Context

Fix security vulnerabilities, we_alloc is no longer maintained and seems to have a memory leak, hence we will remove this feature and always default to the rust standard allocator.

Does this PR introduce a breaking change?

• Yes
• No

This PR has two breaking changes:

• wee_alloc feature flag is removed;
• Rust edition goes from 2018 to 2021, to take advantage of the new default rust WASM allocator.
• Fixes the CI to rust version 1.72.x

Which merge strategy will you use?

• Squash
• Rebase (REVIEW COMMITS)