Move to Swift 5.9 as the minimum version

[alexdeem]

• Move to Swift 5.9 as the minimum version
• Opt in to swift 5.9 rules for swiftformat

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.83%. Comparing base (5f693e8) to head (0cc13b1).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #59      +/-   ##
===========================================
- Coverage    98.83%   98.83%   -0.00%     
===========================================
  Files            6        6              
  Lines          342      341       -1     
===========================================
- Hits           338      337       -1     
  Misses           4        4              

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