serial write hardening: bound the overlapped-write wait (500ms + CancelIo + 3s sick window) -- a dropped USB-serial link parked the game forever in GetOverlappedResult (ALPHA-MR minidump: SendPacket <- RIO ctor); txTO= counter joins the [rio] health line

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

engine/MUNGA_L4/L4RIO.cpp

@@ -1267,6 +1267,8 @@ static unsigned gRioRRetryMirror   = 0;
 static unsigned gRioRAbandonMirror = 0;
 static unsigned gRioRFullMirror    = 0;
 
+extern "C" unsigned BTPcspakTxTimeouts();	// L4PCSPAK.cpp: bounded-write stat
+
 //
 // The printer half -- called from BTGlassPanels_Tick beside the [glassperf]
 // report (a stream site that prints every second without incident), NEVER
@@ -1326,6 +1328,7 @@ extern "C" void
 			<< " age=" << (gRioLastReplyTick != 0
 							? (now - gRioLastReplyTick) : 0)
 			<< "ms stalls=" << gRioStallCount
+			<< " txTO=" << BTPcspakTxTimeouts()
 			<< " lineErr=" << gRioLineErrMirror
 			<< " overrun=" << gRioOverrunMirror
 			<< " abandon=" << gRioAbandonMirror