Add IO stats to avif to see how large OBUs are after read/write
diff --git a/src/write.c b/src/write.c
index 9719a7b..700867e 100644
--- a/src/write.c
+++ b/src/write.c
@@ -285,6 +285,13 @@
 
     avifStreamFinishBox(&s, meta);
     avifStreamFinishWrite(&s);
+
+    // -----------------------------------------------------------------------
+    // IO stats
+
+    image->ioStats.colorOBUSize = colorOBU.size;
+    image->ioStats.alphaOBUSize = alphaOBU.size;
+
     result = AVIF_RESULT_OK;
 
     // -----------------------------------------------------------------------