Changes

* Compile speed and memory usage

** Incremental compilation ([https://github.com/rust-lang/rust/labels/A-incr-comp A-incr-comp issues], [https://github.com/rust-lang/rust/labels/WG-compiler-incr WG-compiler-incr issues])

** [https://users.rust-lang.org/t/contract-opportunity-mozilla-distributed-compilation-cache-written-in-rust/13898 Distributed compilation cache]

** [https://github.com/rust-lang/cargo/issues/1997 Artifact caching]?