Use cache mounts instead of --clean?

[dholth]

Docker includes a cache mounts feature that removes the need to immediately clean conda/yum/etc. installs, accessed like

RUN --mount=type=cache,target=/root/.cache/pip \ pip install -U packages

The given path is preserved between docker invocations (maybe not in the cloud) and is not included in the image. It is only used on any individual RUN line that has the argument.