Effective Rust canisters: optimization

TL;DR: Effective Rust canisters

The Effective Rust Canisters article (first featured in "Best Practices for Canisters in Rust" now available as text) just got a new section on canister optimization.
Thank @dsarlis and @berestovskyy for implementing the performance_counter API (I was waiting for this API to write the new section!) and for their feedback on the article’s first draft.