add channel renderer + try to simplify adapter generics

library/internal/channel-message-renderer.ts

@@ -0,0 +1,13 @@
+import type { Channel } from "./channel"
+import type { Message, MessageOptions } from "./message"
+import { Renderer } from "./renderer"
+
+export class ChannelMessageRenderer extends Renderer {
+  constructor(private channel: Channel) {
+    super()
+  }
+
+  protected createMessage(options: MessageOptions): Promise<Message> {
+    return this.channel.send(options)
+  }
+}