Fix methods

[soutaro]

#39 told me that BasicObject does not have several methods including method, class, or singleton_class. So, we should extract these methods beforehand.

The patch includes a fix to extract is_a? from Kernel, not Object. And it adds PP for future printf debugging.

[hanachin]

Following test will raise NoMethodError when RBS_TEST_LOGLEVEL=debug at these lines because BasicObject doesn't have inspect method.

class BasicObjectTest < StdlibTest
  target BasicObject
  using hook.refinement

  def test_instance_eval
    BasicObject.new.instance_eval {  }
  end
end

https://github.com/ruby/ruby-signature/blob/2a47654e84c0e06e67fe6f2c0b6964b498d167ec/lib/ruby/signature/test/hook.rb#L168
https://github.com/ruby/ruby-signature/blob/2a47654e84c0e06e67fe6f2c0b6964b498d167ec/lib/ruby/signature/test/hook.rb#L177
https://github.com/ruby/ruby-signature/blob/2a47654e84c0e06e67fe6f2c0b6964b498d167ec/lib/ruby/signature/test/hook.rb#L187
https://github.com/ruby/ruby-signature/blob/2a47654e84c0e06e67fe6f2c0b6964b498d167ec/lib/ruby/signature/test/hook.rb#L203

[soutaro]

@hanachin No #inspect ... 😱 Thanks.

[hanachin]

looks good to me 🌾