Improve package loadable

[balloob]

Description:

Started digging deeper into the package loadable code. In my dev environtment running in a virtualenv, which has ~200 packages, 0.5 of 0.74 seconds startup time were spend inside package_loadable 🤕

Added a cache and moving most checks into the event loop, we're doing a ton less I/O now and it's down to 0.04s on my machine, x12 improvement to check if packages need to be installed! If you are running Home Assistant from a slower disk, I expect an even better boost.

Now on my machine: Home Assistant initialized in 0.44s 😎

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[pvizeli]

Good work!