Split a retried drop out of close, and range-check the backoff

`close` fires only where nothing will bring the session back; a drop the
reconnect loop will retry is `disconnected`, pairing with `reconnected`.
`minDelay: 0` never doubles, so the backoff never started — both delays
are range-checked now, and only `false` spells reconnect off.

src/session.ts

@@ -376,7 +376,12 @@ export class Session extends EventEmitter<SessionEvents> {
 		this.pending.settleAll(new Error('Session closed before a response arrived'));
 		this.incoming.clear();
 		this.sock.destroy();
-		this.emit('close');
+		this.emit(this.retrying() ? 'disconnected' : 'close');
+	}
+
+	/** A drop the loop will bring the session back from is a disconnect, not the end of it. */
+	private retrying(): boolean {
+		return this.reconnectLoop !== undefined && !this.reconnectLoop.isStopped();
 	}
 
 	private nextConcatReference(): number {