Replace decode_image with decode_comprehensive, which exercises
per-IFD via a probe_directory helper:
- Tag iteration and value parsing for every tag
- SubIFD, EXIF, and GPS directory traversal via read_directory
- Image metadata (dimensions, colortype, color_map, chunk info)
- Layout queries (image_buffer_layout, image_chunk_buffer_layout)
- Per-chunk reads at first and last indices
- Full image decode via read_image
Three IFD traversal strategies:
- Linear iteration via next_directory (tolerates invalid
intermediate IFDs)
- Random-access via seek_to_directory (find_nth_ifd code path)
- Image-aware random-access via seek_to_image
Dictionary covers classic TIFF and BigTIFF byte order marks, and
common IFD tags in both LE and BE (image geometry, strips, tiles,
SubIFD, EXIF, GPS, ColorMap).
Strict resource limits (512 KB decode/intermediate, 64 KB IFD).
Bounded iteration (max 8 linear, max 4 seek).
Format-specific dictionary with LE/BE byte order marks, TIFF magic
number, and common IFD tag numbers as 2-byte LE and BE pairs.
Also add coverage to fuzz/.gitignore.
Lilith River