persist TAStudio max undo levels to config

- resolves #3478

src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.MenuItems.cs

@@ -795,7 +795,7 @@ namespace BizHawk.Client.EmuHawk
 
 				if (val > 0)
 				{
-					CurrentTasMovie.ChangeLog.MaxSteps = val;
+					Settings.MaxUndoSteps = CurrentTasMovie.ChangeLog.MaxSteps = val;
 				}
 			}
 		}

src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.cs

@@ -116,6 +116,7 @@ namespace BizHawk.Client.EmuHawk
 			public bool BindMarkersToInput { get; set; }
 			public bool CopyIncludesFrameNo { get; set; }
 			public TAStudioPalette Palette { get; set; }
+			public int MaxUndoSteps { get; set; } = 100;
 		}
 
 		public TAStudio()
@@ -541,6 +542,7 @@ namespace BizHawk.Client.EmuHawk
 			movie.InputRollSettingsForSave = () => TasView.UserSettingsSerialized();
 			movie.BindMarkersToInput = Settings.BindMarkersToInput;
 			movie.GreenzoneInvalidated = GreenzoneInvalidated;
+			movie.ChangeLog.MaxSteps = Settings.MaxUndoSteps;
 			movie.PropertyChanged += TasMovie_OnPropertyChanged;
 
 			SuspendLayout();

src/BizHawk.Client.EmuHawk/tools/TAStudio/UndoHistoryForm.cs

@@ -164,7 +164,7 @@ namespace BizHawk.Client.EmuHawk
 
 		private void MaxStepsNum_ValueChanged(object sender, EventArgs e)
 		{
-			Log.MaxSteps = (int)MaxStepsNum.Value;
+			_tastudio.Settings.MaxUndoSteps = Log.MaxSteps = (int)MaxStepsNum.Value;
 		}
 	}
 }