NB: While using a higher C# version with lower framework version is possible, it's generally advised against because C# syntax may map to .NET types not available in older versions such as .NET Standard 2.1.
This change does not invite the codebase to upgrade to newer types, but rather take advantage of syntax sugar (such as file-scoped namespaces, when this project was updated to C# 10) that does not effect the compiled result.
However, this change does open up the possibilities to add extension methods for the "generic math" interfaces (made possible by static interface members), and these upcoming methods will be targeted to .NET 7 or greater **ONLY**.
- Use C# 9 (instead of C# 8)
- Removed Rozlynator and StyleCop analysers
- Update line length to 130
- using directives now go outside namespace
- Enforce US english
- Enforce braces for single statements
- Implicit type where appropriate
