TODO: the algorithm and caching mechanism used by pacquet install without lockfile is unnecessarily complicated

[KSXGitHub]

The current algorithm only symlinks after tarball is downloaded, extracted, and installed. But symlink operation does not require target to exist.

There is also a hidden assumption that the linking of dependencies of a package to be only performed after the package is installed. This makes the caching mechanism more complicated and convoluted than necessary: If a cache key is hit, it will wait for the cache value to be available to links its own dependencies (so-called auto_import in the code).

Separating the symlink operations from the tarball download/extract/install operation could potentially speed up the process. It would also allow early returns in case of a cache hit, simplifying the data structure of Cache and the algorithm used by the caching mechanism.

This endeavor should be easier after #128 is completed.