Recreating Stimulus: targets, actions and reactive values

Part 2 of a series on recreating Stimulus from scratch, covering how targets, actions, and reactive values work under the hood. Targets are implemented using Object.defineProperty to create dynamic getters that query the DOM live. Actions use event delegation with a single document-level listener per event type, parsing data-action descriptors with simple string splitting. Values use Object.defineProperty with both getter and setter to sync state to DOM attributes, fire change callbacks, and handle type coercion for Number, Boolean, Array, and Object types.