Fix memory leak in JPEG EXIF rotation (rotate90/rotate270)

[iurisilvio]

Fixes #2572.

The rotate90 and rotate270 lambdas in Image::rotatePixels allocate a temporary unrotated buffer via new uint8_t[n_bytes] but never free it. Every JPEG decoded with EXIF orientation 5, 6, 7, or 8 leaks the full rotated pixel buffer (width * height * 4 bytes) on each loadImage call.

For a 1200×1800 test image (recurser/exif-orientation-examples Landscape_6.jpg, EXIF Orientation=6), 100 sequential loads leak 837 MiB (~8.4 MiB/iter, matching width * height * 4 = 8,640,000 bytes exactly). After this fix, RSS plateaus after the first ~10 iterations and stays flat.

The full repro script and observed numbers are in #2572.

Diff is one line added to each lambda:

   auto rotate90 = [](uint8_t* pixels, int width, int height, int channels) {
     ...
+    delete[] unrotated;
   };

   auto rotate270 = [](uint8_t* pixels, int width, int height, int channels) {
     ...
+    delete[] unrotated;
   };