unpack_strategy/directory: use mv for nested unpack

[cho-m]

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mv should preserve hardlinks and allow faster unpack on the same filesystem. A secondary pass is done with cp to copy over attributes onto any existing directories.

We only run this for nested unpacks as most direct Directory strategy usage is for repositories where moving files breaks existing code.

There are also potential user issues that could be due to Apple's cp -l on specific macOS versions. Can consider re-adding cp -l with improved fallback handling if there is noticeable advantages.

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This improves performance when pouring bottles if user has brew installed on same filesystem as /tmp directory (~1.2-1.4x when tested via brew reinstall which means direct brew install).

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macOS mv man page says:

     As the rename(2) call does not work across file systems, mv uses cp(1) and rm(1) to accomplish the move.  The
     effect is equivalent to:

           rm -f destination_path && \
           cp -pRP source_file destination && \
           rm -rf source_file

Which should essentially be similar to cp -pR when combined with other logic.

[cho-m]

Will need to think about this a bit more in relation to how we are "unpacking" git repositories.

[MikeMcQuaid]

Worth a try once 🟢 and you're ready, thanks!

[cho-m]

I need to update these tests to run on both move: true and move: false.