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/index.ts

@@ -18,7 +18,7 @@ export {
 	pduToObj,
 } from './pdu.ts';
 
-export { maxPduLength } from './pdu-refusal.ts';
+export { maxPduLength, PduRefusedError } from './pdu-refusal.ts';
 
 export {
 	bitCount,
@@ -62,6 +62,7 @@ export type { ConstGroup, MessageState } from './defs/constants.ts';
 export type { Encoding, EncodingName } from './defs/encodings.ts';
 export type { ErrorName } from './defs/errors.ts';
 export type { PduObject, PduObjectInput, TlvInput } from './pdu.ts';
+export type { PduHeader } from './pdu-refusal.ts';
 export type { SplitOptions } from './message.ts';
 export type { Tlv, TlvDefinition, TlvName } from './defs/tlvs.ts';
 export type { DestAddress, ParamValue, UnsuccessSme, WireType } from './defs/types.ts';