.NET 7 Generic math support

[tompazourek]

• Add support for .NET 7 generic math #47

TODO

• Span-based TryFormat
• Span-based Parse and TryParse
• % operator
• TryConvertFrom* and TryConvertTo* methods
• Tests

[codecov]

Codecov Report

Merging #52 (3480d69) into master (2aef85d) will decrease coverage by 0.54%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #52      +/-   ##
==========================================
- Coverage   55.17%   54.63%   -0.54%     
==========================================
  Files          17       17              
  Lines         812      820       +8     
  Branches      181      181              
==========================================
  Hits          448      448              
- Misses        330      338       +8     
  Partials       34       34              

Impacted Files	Coverage Δ
src/Rationals/Formatting.cs	90.90% <0.00%> (-2.12%)	⬇️
src/Rationals/Operators.cs	73.33% <0.00%> (-11.29%)	⬇️
src/Rationals/Parsing.cs	63.07% <0.00%> (-5.26%)	⬇️