[stacked] Struct API and bullet stream for Bundle install layer (#332)

* Introduce meta struct for holding layer ref results

* Rename generic to match M for metadata style

* Rename metadata generic

* Use Meta<M> to return old cached data

Meta<M> acts like a String for purposes of printing, but can optionally contain old metadata if the programmer needs it. This is useful for the "bundle install" layer which stores information in it's cache that is not used for cache invalidation but rather to determine whether or not it can skip running `bundle install`.

* Rename structs

* Move docs to module

* Update docs

* Move metadata type alias to top of file

* Update const name and add docs

* Add docs

* Implement MetadataDiff

This diff will eventually control caching logic

* Test caching logic

* Refactor bundle install command invocation

* Group imports

* Stub handle function with no logic

* Build install state from old cache data

* Rename UpdateState to InstallState

* Call bundle install from handle function

* Replace layer with struct API call

* Rename function

* Remove unused imports

* Move buildpack logging to the top of main

* Remove import

* Move logic out of function

* Replace commons logging with bullet stream

* Clippy