refactor: remove internal ChatSessionState from public exports

ChatSessionState is an implementation detail of the transport's
session tracking. Users don't need to access it since the sessions
map is private.

Co-authored-by: Eric Allam <eric@trigger.dev>

packages/ai/src/index.ts

@@ -1,3 +1,3 @@
 export { TriggerChatTransport, createChatTransport } from "./transport.js";
-export type { TriggerChatTransportOptions, ChatTaskPayload, ChatSessionState } from "./types.js";
+export type { TriggerChatTransportOptions, ChatTaskPayload } from "./types.js";
 export { VERSION } from "./version.js";