Fix navigation crash

[andreia-ferreira]

Fixes #3846

The crash could be reproduced with the following steps:
1 - Enable 'Don't keep activities' on Developer Settings
2 - Turn off network connection
3 - Start data collection and complete a few tasks
4 - Put the app on the background
5 - Go back to Ground
6 - Crash

After the app was killed in the background, MainViewModel was recreated and immediately received the signed-in user again. When in offline mode, the MainVM would be recreated and get the user right away since there was no connection for updateRemoteUserInfo. Offline this happened almost instantly, because updateRemoteUserInfo returns early when there is no connection instead, navigation then proceeded to the Home screen, popping the restored back stack. So when the data collection screen tried to fetch its VM from the back stack it crashed.

Now the MainActivity will only proceed with this rerouting if the user is still on startup or signIn screen so a restored screen is left alone.
There is also a small refactor changing MainUiState to MainUiEffect since it mostly works with one time events rather than a screen state.

@shobhitagarwal1612 PTAL?

[codecov]

Codecov Report

❌ Patch coverage is 72.00000% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.40%. Comparing base (44bcd71) to head (7c1ca33).

Files with missing lines	Patch %	Lines
...rg/groundplatform/android/ui/main/MainViewModel.kt	68.00%	5 Missing and 3 partials ⚠️
...org/groundplatform/android/ui/main/MainActivity.kt	73.91%	1 Missing and 5 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3853      +/-   ##
============================================
+ Coverage     67.37%   67.40%   +0.03%     
- Complexity     1838     1840       +2     
============================================
  Files           407      407              
  Lines         10755    10759       +4     
  Branches       1418     1420       +2     
============================================
+ Hits           7246     7252       +6     
+ Misses         2763     2762       -1     
+ Partials        746      745       -1     

Files with missing lines	Coverage Δ
...org/groundplatform/android/ui/main/MainUiEffect.kt	100.00% <100.00%> (ø)
...org/groundplatform/android/ui/main/MainActivity.kt	43.82% <73.91%> (+6.91%)	⬆️
...rg/groundplatform/android/ui/main/MainViewModel.kt	65.57% <68.00%> (-0.53%)	⬇️

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