refactor(core): CORE-02 type emitter maps and fix nested once dispatch

test/types/emitter-source.ts

@@ -0,0 +1,42 @@
+import type { Events } from 'artplayer'
+import Emitter from '../../packages/artplayer/src/utils/emitter'
+
+const symbol = Symbol('message')
+interface Messages {
+  ready: []
+  value: [count: number, label?: string]
+  readonly: readonly [value: number]
+  [symbol]: [message: string]
+}
+class TypedEmitter extends Emitter<Messages> {
+  count = 0
+}
+const events = new TypedEmitter()
+const context = { total: 0 }
+const chain: TypedEmitter = events.on('value', function (count, label) {
+  this.total += count
+  label?.toUpperCase()
+}, context).once('ready', () => {}).emit('value', 1).off('ready')
+events.emit(symbol, 'message')
+events.emit('readonly', 1)
+const playerEvents = new Emitter<Events & Record<string, unknown[]>>()
+playerEvents.emit('setBar', 'loaded', 0.5)
+playerEvents.emit('custom:event', { extra: true })
+// @ts-expect-error Known events retain their payload types with open custom names.
+playerEvents.emit('setBar', 'invalid', 0.5)
+// @ts-expect-error A declared map rejects unknown names.
+events.emit('missing')
+// @ts-expect-error Payload types are correlated with the event name.
+events.emit('value', 'one')
+// @ts-expect-error Required payloads cannot be omitted.
+events.emit('value')
+// @ts-expect-error Empty events reject extra values.
+events.emit('ready', 1)
+// @ts-expect-error Listener arguments must match the event.
+events.on('value', (count: string) => count)
+// @ts-expect-error Explicit receiver types must agree with the provided context.
+events.on('ready', contextListener, { total: 'zero' })
+function contextListener(this: { total: number }) {
+  return this.total
+}
+void chain