Defer vsync_offset application

- Apply vsync_offset only during the vertical retrace period for a more accurate result
- Change the calculation of displine_offs and remove redundant checks around rendering calls
- Remove unnecessary clamping logic for crtc[7]
- Remove a hack from the previous commit by correctly triggering VSYNC processing when the vertical counter matches the actual crtc[7]

src/include/86box/m_tandy.h

@@ -41,6 +41,7 @@ typedef struct t1kvid_t {
     bool     baseline_ready;
     int      hsync_offset;
     int      vsync_offset;
+    int      vsync_offset_pending;
 
     int      linepos;
     int      displine;