Formatters cannot be set/got when your implementation does not support Ractors

I was not passing some MRI pattern matching specs and realized that it was not setting the NullFormatter. It is because formatter requires Ractors to work.

I did a quick fix:

  # Returns the currently set formatter. By default, it is set to +DidYouMean::Formatter+.
  def self.formatter
    storage = defined?(Ractor) ? Ractor : Thread
    storage.current[:__did_you_mean_formatter__] || Formatter
  end

  # Updates the primary formatter used to format the suggestions.
  def self.formatter=(formatter)
    storage = defined?(Ractor) ? Ractor : Thread
    storage.current[:__did_you_mean_formatter__] = formatter
  end

but I suspect this is not right. This is a global setting and not just a thread-specific one...or is it?

Start by examining the formatter getter and setter shown in the issue, including how they use Ractor or Thread storage. Determine whether formatter state should be global or thread-specific, then verify that setting and reading the formatter works on implementations without Ractors and that the relevant pattern-matching specs pass.