Codebase Improvements

• Replace speedtest Mac dependency for speedtest-cli
• Lint the codebase on both MacOS Big Sur & Debian 11
• Add option for reloading the menu after each test

Existing users - note for updating:

• Delete ~/.nettest directory (will rebuild caches / do a first-run check)
  • OR
• Add the following line to your existing ~/.nettest/config.conf:

RELOAD_MENU=0

• Reload menu details