GildedRose now resolves each item to its strategy and applies it; all
rules live in the strategies. The original one-arg constructor keeps
working by delegating to ItemUpdaterFactory.Default(); a second
constructor allows injecting a custom IItemUpdaterFactory.
No behaviour change: the ThirtyDays approval snapshot and all
existing-type spec tests pass unchanged.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
