feat(caching): Cache clojure dependencies

[mainej]

Summary

Fixes #485.

Projects that contain a deps.edn file are compiled by the Clojure CLI. (This is analogous to a Gemfile, which signals that a project is built with ruby.)

This PR speeds up builds of these projects by caching their dependencies. The following directories are now cached:

• .m2 As a JVM language, most Clojure dependencies are stored in the global .m2 directory.
• .gitlibs The Clojure CLI can also download dependencies directly from git repositories rather than from a package manager. It saves these downloads in the .gitlibs directory.
• .cpcache Clojure uses the .cpcache directory to avoid unnecessarily re-calculating the JVM classpath. Caching this directory won't prevent downloads, but does improve build time slightly.

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