Gem::Ext::CargoBuilder#so_ext

# File tmp/rubies/ruby-3.3.0/lib/rubygems/ext/cargo_builder.rb, line 320
def so_ext
  return RbConfig::CONFIG["SOEXT"] if RbConfig::CONFIG.key?("SOEXT")

  if win_target?
    "dll"
  elsif darwin_target?
    "dylib"
  else
    "so"
  end
end