Migrate all @layerstack/svelte-actions to @layerstack/svelte-attach package and use callbacks instead of events #50

Svelte 5.29 released new {@attach ...} syntax which are an improvement over actions including being reactive by default, conditionally applied, and passed to components (via spread/etc)

While updating, we will also remove the events and instead use callbacks. This allows removing svelteHTML types, which doesn't great and is not discoverable.

See movable within LayerChart (will replace LayerStack impl) for an example.