feat(#637): show unknown guidelines as green

[tamslo]

Closes #637

Changes

• Show unknown warning as green, not gray
• Refactoring: introduce method to get warning level from guideline or WarningLevel.none, if guideline is ´null´

[codecov]

Codecov Report

Patch coverage: 81.25% and project coverage change: +0.09% 🎉

Comparison is base (2eb5646) 57.08% compared to head (3ff1a72) 57.18%.
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #659      +/-   ##
==========================================
+ Coverage   57.08%   57.18%   +0.09%     
==========================================
  Files          75       76       +1     
  Lines        1715     1719       +4     
==========================================
+ Hits          979      983       +4     
  Misses        736      736              

Flag	Coverage Δ
app	54.00% <81.25%> (+0.11%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
app/lib/common/constants.dart	40.00% <ø> (ø)
app/lib/common/models/drug/drug.dart	37.50% <0.00%> (-1.64%)	⬇️
app/lib/common/models/drug/warning_level.dart	100.00% <100.00%> (ø)
...pages/drug/widgets/annotation_cards/guideline.dart	91.66% <100.00%> (ø)
app/lib/common/theme.dart	64.44% <100.00%> (+0.80%)	⬆️
app/lib/common/utilities/guideline_utils.dart	100.00% <100.00%> (ø)
...ommon/widgets/drug_list/drug_items/drug_cards.dart	93.33% <100.00%> (+2.02%)	⬆️

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