RemoveUnusedMethod check will consider methods private if they are below the private flag of a nested class

[BenMusch]

Example:

class Foo
  class Bar
    def public_nested_method; end

    private
    
    def private_nested_method; end
  end

  def public_method; end
end

In this example, the method public_method would be considered private, because it is below the "private" flag in the nested object, even though it is actually a public method