Improve error handling in the scan survey QR flow

[andreia-ferreira]

This PR improves error handling when there are network issues while scanning a survey QR code, or if there are problems launching the ML kit barcode scanner. Changes include:

• new ScannerUnavailable error type for when the ML Kit barcode scanner module fails to install or is unavailable on the device
• updated toSurveySelectorError() to distinguish network-related failures from generic ones by mapping them to the existing Timeout error type, which already prompts the user to check their connection.

@shobhitagarwal1612 PTAL?

[codecov]

Codecov Report

❌ Patch coverage is 64.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.03%. Comparing base (19bdde7) to head (284b305).

Files with missing lines	Patch %	Lines
...droid/ui/surveyselector/SurveySelectorViewModel.kt	69.56%	3 Missing and 4 partials ⚠️
...ndroid/ui/surveyselector/SurveySelectorFragment.kt	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3732      +/-   ##
============================================
- Coverage     68.06%   68.03%   -0.03%     
- Complexity     1609     1613       +4     
============================================
  Files           370      370              
  Lines          9513     9526      +13     
  Branches       1238     1246       +8     
============================================
+ Hits           6475     6481       +6     
- Misses         2360     2365       +5     
- Partials        678      680       +2     

Files with missing lines	Coverage Δ
...m/android/ui/surveyselector/SurveySelectorEvent.kt	100.00% <ø> (ø)
...ndroid/ui/surveyselector/SurveySelectorFragment.kt	70.37% <0.00%> (-5.63%)	⬇️
...droid/ui/surveyselector/SurveySelectorViewModel.kt	79.34% <69.56%> (-3.37%)	⬇️

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