Strict concurrency

[roanutil]

• Bump minimum swift tools version to 5.8
• Enable strict concurrency checking
• Remove Xcode 14.2/Swift 5.7 and add Xcode 15.0/Swift 5.9 test strategies
• Bump swiftformat Swift version to 5.8
• Simplify Swift settings in manifest and add other Swift 6.0 settings
• Run swiftformat (updated file header dates)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ee02af2) 81.34% compared to head (903e208) 81.23%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
- Coverage   81.34%   81.23%   -0.12%     
==========================================
  Files          23       23              
  Lines        1410     1407       -3     
==========================================
- Hits         1147     1143       -4     
- Misses        263      264       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[r-jarvis]

There are a few more upcoming flags that aren't in this list. Did we want the full list here if this setting is going to mimic Swift 6.0? The 2 specifically I was looking at were:

https://github.com/apple/swift-evolution/blob/main/proposals/0413-typed-throws.md
https://github.com/apple/swift-evolution/blob/main/proposals/0418-inferring-sendable-for-methods.md

[roanutil]

Those would require another increase in the minimum Swift version and may only be available in 5.10+. I don't think either of them would make much difference for this package anyway.