Raise minimum Swift version to 5.8

[ctreffs]

Description

• Raise Swift tools version to 5.8
• Update README
• Add Swift version file
• Format code for 5.8
• Update swiftformat config

Checklist

• [x] I've read the Contribution Guidelines
• [x] I've followed the coding style of the rest of the project.
• [x] I've added tests covering all new code paths my change adds to the project (to the extent possible).
• [ ] I've added benchmarks covering new functionality (if appropriate).
• [x] I've verified that my change does not break any existing tests or introduce unexpected benchmark regressions.
• [x] I've updated the documentation (if appropriate).

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 88.88889% with 2 lines in your changes missing coverage. Please review.

Project coverage is 96.91%. Comparing base (2c1c588) to head (3a3c15d). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #67 +/- ## ======================================= Coverage 96.91% 96.91% ======================================= Files 24 24 Lines 1069 1069 ======================================= Hits 1036 1036 Misses 33 33 ```