[bug] If packageDir does not exist, run Install

[blast-hardcheese]

Why

During testing, rm -rf .pythonlibs followed by a Run skips package install completely:

Turns out this is because we don't verify the package directory actually exists

~/2024-02-15-venv-test$ upm show-package-dir
/home/runner/2024-02-15-venv-test/.pythonlibs
~/2024-02-15-venv-test$ du -sh $(upm show-package-dir)
du: cannot access '/home/runner/2024-02-15-venv-test/.pythonlibs': No such file or directory

What changed

• If the package directory isn't present, ignore the cache and run install.

Test plan

[ryantm]

Nice, I think I've hit this before long ago.