Add render throttle to decouple parse throughput from GDI overhead

During bulk serial data flow, renders are capped at ~20fps (50ms interval)
so the ANSI parser can run at full speed without blocking on FlipToScreen.
When idle, renders immediately for interactive responsiveness.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

delphi/TESTMAIN.PAS

@@ -165,13 +165,18 @@ end;
 
 
 procedure TMainForm.Run;
+const
+  RenderMs = 50;   { Minimum ms between renders during bulk flow (20 fps) }
 var
   Msg:            TMsg;
   S:              string;
   HasData:        Boolean;
+  Now:            Longint;
+  LastRenderTick: Longint;
 begin
   Show;
   FDone          := False;
+  LastRenderTick := GetTickCount;
   while not FDone do
   begin
     { Process all pending Windows messages (keyboard, paint, scrollbar) }
@@ -218,9 +223,16 @@ begin
     if FDone then
       Break;
 
-    { Tick blink (dirties rows if interval elapsed), then render }
+    { Render throttle: during bulk data flow, only render every RenderMs }
+    { to decouple parse throughput from GDI overhead.  When idle, render  }
+    { immediately for interactive responsiveness.                         }
+    Now := GetTickCount;
+    if (not HasData) or (Now - LastRenderTick >= RenderMs) then
+    begin
       FAnsi.TickBlink;
       FAnsi.FlipToScreen;
+      LastRenderTick := Now;
+    end;
 
     { Yield CPU to other apps when no serial data is flowing.          }
     { PM_NOYIELD keeps message draining fast; Yield here gives other   }