Enable Swift 6 Language Mode

[Supereg]

Enable Swift 6 Language Mode

♻️ Current situation & Problem

This PR enables the Swift 6 Language Mode and fixes some concurrency issues.

⚙️ Release Notes

• Enabled Swift 6 Language Mode

📝 Code of Conduct & Contributing Guidelines

By submitting creating this pull request, you agree to follow our Code of Conduct and Contributing Guidelines:

• I agree to follow the Code of Conduct and Contributing Guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.84%. Comparing base (03d82c2) to head (ea95583).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #14      +/-   ##
==========================================
+ Coverage   54.79%   54.84%   +0.05%     
==========================================
  Files          21       21              
  Lines         982      983       +1     
==========================================
+ Hits          538      539       +1     
  Misses        444      444              

Files with missing lines	Coverage Δ
...iMedication/Extensions/String+LocalizedError.swift	0.00% <ø> (ø)
...ziMedication/Extensions/UIDatePicker+SwiftUI.swift	0.00% <ø> (ø)
.../SpeziMedication/MedicationSettingsViewModel.swift	100.00% <ø> (ø)
Sources/SpeziMedication/Models/Weekdays.swift	3.80% <ø> (ø)
...ziMedication/ModifyMedication/EditMedication.swift	100.00% <100.00%> (ø)
...edication/ModifyMedication/ScheduleFrequency.swift	0.00% <ø> (ø)

... and 2 files with indirect coverage changes

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[PSchmiedmayer]

Thank you for all the updates @Supereg!