fix(types): mark type parameters as optional (#1101)

Some types which end-users could be using, declare the type parameters as requried, when in fact they are entirely optional.

This arises when users try to use the event handler code on it's own

src/event-handler/index.ts

@@ -16,7 +16,7 @@ import {
 import { receiverHandle as receive } from "./receive.js";
 import { removeListener } from "./remove-listener.js";
 
-export interface EventHandler<TTransformed> {
+export interface EventHandler<TTransformed = unknown> {
   on<E extends EmitterWebhookEventName>(
     event: E | E[],
     callback: HandlerFunction<E, TTransformed>,
@@ -38,7 +38,7 @@ export interface EventHandler<TTransformed> {
   receive(event: EmitterWebhookEvent | WebhookError): Promise<void>;
 }
 
-export function createEventHandler<TTransformed>(
+export function createEventHandler<TTransformed = unknown>(
   options: Options<TTransformed>,
 ): EventHandler<TTransformed> {
   const state: State = {

src/types.ts

@@ -47,12 +47,12 @@ type TransformMethod<T> = (event: EmitterWebhookEvent) => T | PromiseLike<T>;
 
 export type HandlerFunction<
   TName extends EmitterWebhookEventName,
-  TTransformed,
+  TTransformed = unknown,
 > = (event: EmitterWebhookEvent<TName> & TTransformed) => any;
 
 export type RemoveHandlerFunction<
   TName extends EmitterWebhookEventName | "*",
-  TTransformed,
+  TTransformed = unknown,
 > = (event: EmitterWebhookEvent<Exclude<TName, "*">> & TTransformed) => any;
 
 type Hooks = {