Refactor: Use pressure-based calculations in GasPlanner and OxygenToxicityCalculator

[Rolf-Smit]

GasPlanner and OxygenToxicityCalculator now use pressures directly. Meter-based helper functions on the Gas type have been replaced with pressure-based ones.

Required for: #49

[codecov-commenter]

Codecov Report

❌ Patch coverage is 54.09836% with 28 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.14%. Comparing base (80009a5) to head (aa039c7).

Files with missing lines	Patch %	Lines
.../app/abysner/domain/diveplanning/model/DivePlan.kt	0.00%	8 Missing ⚠️
...r/presentation/component/GasPropertiesComponent.kt	46.15%	3 Missing and 4 partials ⚠️
...reens/planner/segments/SegmentPickerBottomSheet.kt	30.00%	2 Missing and 5 partials ⚠️
...otech/app/abysner/domain/gasplanning/GasPlanner.kt	70.00%	0 Missing and 3 partials ⚠️
...ion/screens/planner/DiveEditorViewModelDelegate.kt	0.00%	0 Missing and 1 partial ⚠️
...resentation/screens/planner/PlanScreenViewModel.kt	50.00%	0 Missing and 1 partial ⚠️
...n/org/neotech/app/abysner/domain/core/model/Gas.kt	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #180      +/-   ##
==========================================
- Coverage   70.15%   70.14%   -0.02%     
==========================================
  Files         145      145              
  Lines        7847     7840       -7     
  Branches      977      978       +1     
==========================================
- Hits         5505     5499       -6     
+ Misses       1851     1849       -2     
- Partials      491      492       +1     

Flag	Coverage Δ
domain	78.13% <63.63%> (-0.02%)	⬇️
presentation	68.12% <42.85%> (-0.01%)	⬇️

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