The BestSet chooses the best available method to query a remote index.
It combines IndexSet and APISet
Creates a BestSet for the given sources or Gem::sources if none are specified. sources must be a Gem::SourceList.
# File ruby-3.1.2/lib/rubygems/resolver/best_set.rb, line 12
def initialize(sources = Gem.sources)
super()
@sources = sources
end