fix separator conflict in mame dipswitch option code

"@" was used as part of a description string, breaking the parsing. Surely no description includes a newline... (is there a better way to do this?)

- closes #4288

src/BizHawk.Emulation.Cores/Arcades/MAME/MAME.ISettable.cs

@@ -93,11 +93,11 @@ namespace BizHawk.Emulation.Cores.Arcades.MAME
 					};
 
 					var DIPSwitchOptions = MameGetString(MAMELuaCommand.GetDIPSwitchOptions(tag, fieldName));
-					var options = DIPSwitchOptions.Split(new[] { '@' }, StringSplitOptions.RemoveEmptyEntries);
+					var options = DIPSwitchOptions.Split('\n');
 					if (options.Length is 0) continue;
 					foreach (var option in options)
 					{
-						var opt = option.Split(new[] { '~' }, StringSplitOptions.RemoveEmptyEntries);
+						var opt = option.Split('~');
 						setting.Options.Add(opt[0], opt[1]);
 					}
 					CurrentDriverSettings.Add(setting);

src/BizHawk.Emulation.Cores/Arcades/MAME/MAME.cs

@@ -433,10 +433,10 @@ namespace BizHawk.Emulation.Cores.Arcades.MAME
 			public static string GetDIPSwitchOptions(string tag, string fieldName) =>
 				"local final = { } " +
 				$"for value, description in pairs(manager.machine.ioport.ports[\"{ tag }\"].fields[\"{ fieldName }\"].settings) do " +
-					"table.insert(final, string.format(\"%d~%s@\", value, description)) " +
+					"table.insert(final, string.format(\"%d~%s\", value, description)) " +
 				"end " +
 				"table.sort(final) " +
-				"return table.concat(final)";
+				"return table.concat(final, '\\n')";
 			public static string GetViewName(string index) =>
 				$"return manager.machine.video.snapshot_target.view_names[{ index }]";
 		}