kcms/mouse: Another batch of code improvements
Avoid spamming the same error three times
Also split things into one-per-line with comments as section headers.
Don't short-circuit on faulty devices
If some device fails mid-list, we should still try to read and write to the rest of the devices that follow it.
Port iterators to std::ranges
Rename methods for consistency with the KCM class
- getConfig -> load
- getDefaultConfig -> defaults
- applyConfig -> save
- isChangedConfig -> isSaveNeeded
- changed -> isSaveNeeded