Fix RCO menu coordinates and smooth video pacing

RCO object positions are screen-center with +Y up, but the renderer drew
them as top-left, pushing menu items off-screen. Convert to top-left in
the 480x272 design space before drawing.

Also use precise parkNanos pacing and reuse per-frame ARGB/WritableImage
buffers to remove the 1.4MB allocations per video frame.

core/src/main/java/dev/quoije/umd/media/YuvConverter.java

@@ -19,7 +19,16 @@ public final class YuvConverter {
                                       byte[] uPlane, int uStride,
                                       byte[] vPlane, int vStride) {
         int[] argb = new int[width * height];
+        yuvj420ToArgb(width, height, yPlane, yStride, uPlane, uStride, vPlane, vStride, argb);
+        return argb;
+    }
 
+    /** Converts into a caller-provided buffer of at least {@code width*height} pixels. */
+    public static void yuvj420ToArgb(int width, int height,
+                                     byte[] yPlane, int yStride,
+                                     byte[] uPlane, int uStride,
+                                     byte[] vPlane, int vStride,
+                                     int[] argb) {
         for (int row = 0; row < height; row++) {
             int yRow = row * yStride;
             int uvRow = (row >> 1) * uStride;
@@ -43,8 +52,6 @@ public final class YuvConverter {
                         | clamp(b);
             }
         }
-
-        return argb;
     }
 
     private static int clamp(int value) {