Add compatibility for iOS 15 and friends

[ptoffy]

Fix #180

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.76%. Comparing base (f26649c) to head (1a73dfe).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #181   +/-   ##
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  Coverage   78.76%   78.76%           
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  Files          60       60           
  Lines        1413     1413           
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  Hits         1113     1113           
  Misses        300      300           

[0xTim]

Do we want to bump this to 12 to line up?

[ptoffy]

There's a few errors around EC keys about missing conformances with .macOS < 13. Also JSONDecoder and JSONEncoder are only Sendable in 13+

[ptoffy]

I mean we can try solving them but not sure it's worth it?

[0xTim]

What are the issues with EC keys? Because surely we'll have the same issues on iOS 15

[0xTim]

I wonder if it's worth being really annoying and adding CI for iOS (including 15) so see what issues we'd hit

[ptoffy]

The thing is Crypto doesn't specify iOS requirements (or any besides macOS) so there's no issues with that

[Joannis]

Thanks! Looks good to me. I'd recommend lowering this as much as feasible, going even back to iOS 13 if possible. You can always use @available annotations if need be for specific features.