Tell a refused PDU apart from a session that failed (#82)

* Regression tests for telling a refused PDU from a failed session

* Export PduRefusedError so a refusal can be told from a session failure

* Document telling a refused PDU from a session failure

* Share the malformed-PDU fixtures and pin that a dead stream is no refusal

* Say once what a refusal is, and why the header type is published

* Fold the refused-response test into the one that already staged it

* Drop the refusal-rate claim the interop finding does not support

* Build a raw PDU one way, sequence number included

* Follow PduRefusedError into pdu-refusal.ts

src/session-options.ts

@@ -1,6 +1,7 @@
 import type { Dlr } from './dlr.ts';
 import type { MessageDlr } from './dlr-merger.ts';
 import type { PduObject } from './pdu.ts';
+import type { PduRefusedError } from './pdu-refusal.ts';
 import type { Result, VoidResult } from './result.ts';
 import type { Session } from './session.ts';
 import type { SmppLog } from './log.ts';
@@ -19,7 +20,7 @@ export type SessionEvents = {
 	incomingPduObj: [PduObject];
 	messageDlr: [MessageDlr];
 	reconnected: [];
-	sessionError: [Error];
+	sessionError: [Error | PduRefusedError];
 	sms: [Sms];
 };