Improve presentation of non-verbose downloads with non-PyPI indexes

[pradyunsg]

Before:

❯ pip download --index-url https://www.piwheels.org/simple --dest /tmp/throwaway revpy
Looking in indexes: https://www.piwheels.org/simple
Collecting revpy
  Using cached https://archive1.piwheels.org/simple/revpy/revpy-0.1.1-py3-none-any.whl (11 kB)
Saved /private/tmp/throwaway/revpy-0.1.1-py3-none-any.whl
Successfully downloaded revpy

After:

❯ pip download --index-url https://www.piwheels.org/simple --dest /tmp/throwaway revpy
Looking in indexes: https://www.piwheels.org/simple
Collecting revpy
  Downloading revpy-0.1.1-py3-none-any.whl (11 kB)
Saved /private/tmp/throwaway/revpy-0.1.1-py3-none-any.whl
Successfully downloaded revpy

This is a notable improvement if you end up mirroring PyPI's artifact structure in a different index, and end up with URLs like https://files.pythonhosted.org/packages/29/a2/d40fb2460e883eca5199c62cfc2463fd261f760556ae6290f88488c362c0/pip-25.1.1-py3-none-any.whl that end up being really verbose for long install sessions.