[codex] split Event owner types

[jderochervlk]

Summary

This extracts the Event-focused portion of PR #270 into a smaller change set.

• Move public Event APIs toward owner modules with Event.t, EventTarget.t, AbortSignal.t, and ExtendableEvent.t.
• Split event name variants into the public EventType module and update call sites.
• Update dependent Web API type records that spread or reference Event shapes to use the new public owner types.
• Update ReScript to the v13 prerelease required by the source shape and adjust iterable return/test usage for ReScript 13.

Why

PR #270 is broad. This PR isolates the Event changes so the Event owner/type-shape updates can be reviewed independently.

Usage Examples

Event names

Before:

let click: EventTypes.eventType = EventTypes.Click
let custom: EventTypes.eventType = EventTypes.Custom("custom-event")

After:

let click: EventType.t = EventType.Click
let custom: EventType.t = EventType.Custom("custom-event")

Event values and listeners

Before:

let event: EventTypes.event = Event.make(~type_="click")
let target: EventTypes.eventTarget = EventTarget.make()

target->EventTarget.addEventListener(EventTypes.Click, (event: EventTypes.event) => {
  event->Event.preventDefault
})

After:

let event: Event.t = Event.make(~type_="click")
let target: EventTarget.t = EventTarget.make()

target->EventTarget.addEventListener(EventType.Click, (event: Event.t) => {
  event->Event.preventDefault
})

Types that include event behavior

Before:

type messagePort = private {
  ...EventTypes.eventTarget,
}

type storageEvent = private {
  ...EventTypes.event,
}

After:

type messagePort = private {
  ...EventTarget.t,
}

type storageEvent = private {
  ...Event.t,
}

Validation

• npm run build
• npm test