Verify device id even if provided in config

[KapJI]

If spotify_device_id is provided in the config, you may still need to launch an app on Chromecast first to wake it up and make it available in the device list.

Why spotify_device_id may be necessary

When Google Home devices are combined into a speaker pair, the Chromecast device name may be different from the Spotify device name. In that case, in device_name, you will want to use the friendly name of the Chromecast device. However, a device with that name won't be found in the list of Spotify devices, and you'll encounter an error. But if you add spotify_device_id, the Chromecast won't need to be woken up.

Other changes in this PR

• Fixed several typing mistakes
• Formatted the edited parts of the code according to Python guidelines
• Removed duplicated code

I would also like to set up some basic CI to check formatting, run black, isort, codespell, and flake8. https://github.com/leikoilja/ha-google-home/ which I maintain can be a good example. Would you support such changes?