Currently, every evergreen task rebuilds test binaries fresh, even when a set of tasks are all running on the same architecture with the same flags. We should investigate building once per arch*flags combo and fetching those artifacts in each task rather than rebuilding.

This has two benefits:

• it'll speed up task execution (compilation is not fast)
• it'll reduce load on cargo, which is increasingly becoming a topic of concern.

AWS CodeArtifact might be an appropriate system to use for caching.