feat: refactor backup related code

[igordanilcenko]

The first iteration of the fix of the Backup feature.
I prepared code for further refactoring and bug fixing:

• Moved domain logic out from views to viewModels
• Made classes more stateless by passing required inputs as arguments instead of storing them in third-party classes

And also made some enhancements:

• Added some useful extension functions
• Renamed some classes and variables meaningfully (e.g. BackupOptions -> BackupOptionType because it is an enum with possible option types)
• Made log messages more informative
• Made some nullable values null-safe
• Moved view state variables to separate immutable UiState classes

Notes:

• I left some TODOs required for continuation of my work