Use deferred method declaration validation

[djberg96]

This PR is largely courtesy of AI. It uses TracePoint in order to defer method declaration validation so that you can make interface declarations at the top of a class like any other module instead of having to define interface methods.

# Sample
require 'interface'

MyInterface = interface do
  required_methods :foo, :bar
end

# Before
class MyClass
  def foo
    puts "foo"
  end

  def bar
    puts "bar"
  end

  # Before you had to define them before implementing the interface
  implements MyInterface
end

# After
class MyClass
  implements MyInterface # AI Magic

  def foo
    puts "foo"
  end

  def bar
    puts "bar"
  end
end