feat: Predownload APK once selected by choice

[oSumAtrIX]

Feature description

After the user selects a version, ReVanced Manager can download the APK file in the background until the patcher screen is reached.

Motivation

This can potentially save time as the download can happen asynchronously.

Additional context

A setting should be provided to enable or disable this functionality. The user should also initially be alerted about this feature. It could suggest enabling "instant downloading" right after selecting the APK or once entering the patcher screen.

Acknowledgements

• [X] This request is not a duplicate of an existing issue.
• [X] I have chosen an appropriate title.
• [X] All requested information has been provided properly.
• [X] The issue is solely related to the ReVanced Manager