Adds a sequence-point test for 72Hz mode.

Which immediately appears to trigger the hsync issue I'm also seeing in manual testing.

OSBindings/Mac/Clock SignalTests/AtariSTVideoTests.mm

@@ -95,11 +95,22 @@ struct VideoTester {
 // MARK: - Sequence Point Prediction Tests
 
 /// Tests that no events occur outside of the sequence points the video predicts.
-- (void)testSequencePoints {
+- (void)testSequencePoints50 {
 	// Set 4bpp, 50Hz.
 	_video->write(0x05, 0x0200);
 	_video->write(0x30, 0x0000);
 
+	[self runSequencePointsTest];
+}
+
+- (void)testSequencePoints72 {
+	// Set 1bpp, 72Hz.
+	_video->write(0x30, 0x0200);
+
+	[self runSequencePointsTest];
+}
+
+- (void)runSequencePointsTest {
 	// Run for [more than] a whole frame making sure that no observeable outputs
 	// change at any time other than a sequence point.
 	HalfCycles next_event;