Refactor imir implementation to match HEIF Draft Amendment 2, which replaces 'axis' with 'mode' and inverts the behavior
diff --git a/src/write.c b/src/write.c
index 1c1d779..6a2474a 100644
--- a/src/write.c
+++ b/src/write.c
@@ -275,8 +275,8 @@
     }
     if (imageMetadata->transformFlags & AVIF_TRANSFORM_IMIR) {
         avifBoxMarker imir = avifRWStreamWriteBox(s, "imir", AVIF_BOX_SIZE_TBD);
-        uint8_t axis = imageMetadata->imir.axis & 0x1;
-        avifRWStreamWrite(s, &axis, 1); // unsigned int (7) reserved = 0; unsigned int (1) axis;
+        uint8_t mode = imageMetadata->imir.mode & 0x1;
+        avifRWStreamWrite(s, &mode, 1); // unsigned int (7) reserved = 0; unsigned int (1) mode;
         avifRWStreamFinishBox(s, imir);
         if (ipma && itemPropertyIndex) {
             ipmaPush(ipma, ++(*itemPropertyIndex), AVIF_TRUE);