chore: replace decode_image fuzz target with comprehensive decoder exerciser

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).

fuzz/tiff.dict

@@ -1,38 +1,139 @@
-# TIFF byte order and magic
+# === File headers ===
+
+# Classic TIFF (LE, BE)
 "\x49\x49\x2A\x00"
 "\x4D\x4D\x00\x2A"
+# BigTIFF (LE, BE) — version 43, 8-byte offsets, different parsing paths
+"\x49\x49\x2B\x00\x08\x00\x00\x00"
+"\x4D\x4D\x00\x2B\x00\x08\x00\x00"
 
-# Common IFD tags as 2-byte LE pairs
-# 256 = ImageWidth
+# === IFD field type codes (2-byte LE) ===
+# Decoder switches on these; wrong types exercise error paths
+
+"\x01\x00"
+"\x02\x00"
+"\x03\x00"
+"\x04\x00"
+"\x05\x00"
+"\x06\x00"
+"\x07\x00"
+"\x08\x00"
+"\x09\x00"
+"\x0A\x00"
+"\x0B\x00"
+"\x0C\x00"
+"\x0D\x00"
+"\x10\x00"
+"\x11\x00"
+"\x12\x00"
+
+# === IFD tag numbers (2-byte LE) ===
+
+# 256=ImageWidth 257=ImageLength 258=BitsPerSample
 "\x00\x01"
-# 257 = ImageLength
 "\x01\x01"
-# 258 = BitsPerSample
 "\x02\x01"
-# 259 = Compression
+# 259=Compression 262=PhotometricInterpretation
 "\x03\x01"
-# 262 = PhotometricInterpretation
 "\x06\x01"
-# 273 = StripOffsets
+# 273=StripOffsets 274=Orientation
 "\x11\x01"
-# 277 = SamplesPerPixel
+"\x12\x01"
+# 277=SamplesPerPixel 278=RowsPerStrip 279=StripByteCounts
 "\x15\x01"
-# 278 = RowsPerStrip
 "\x16\x01"
-# 279 = StripByteCounts
 "\x17\x01"
-# 282 = XResolution
+# 282=XResolution 283=YResolution 284=PlanarConfiguration
 "\x1A\x01"
-# 283 = YResolution
 "\x1B\x01"
+"\x1C\x01"
+# 317=Predictor 320=ColorMap
+"\x3D\x01"
+"\x40\x01"
+# 322=TileWidth 323=TileLength 324=TileOffsets 325=TileByteCounts
+"\x42\x01"
+"\x43\x01"
+"\x44\x01"
+"\x45\x01"
+# 330=SubIfd 338=ExtraSamples 339=SampleFormat
+"\x4A\x01"
+"\x52\x01"
+"\x53\x01"
+# 347=JPEGTables 530=ChromaSubsampling
+"\x5B\x01"
+"\x12\x02"
+# 34665=ExifDirectory 34675=IccProfile 34853=GpsDirectory
+"\x69\x87"
+"\x73\x87"
+"\x25\x88"
+
+# === IFD tag numbers (2-byte BE) ===
 
-# Common IFD tags as 2-byte BE pairs
 "\x01\x00"
 "\x01\x01"
 "\x01\x02"
 "\x01\x03"
 "\x01\x06"
 "\x01\x11"
+"\x01\x12"
 "\x01\x15"
 "\x01\x16"
 "\x01\x17"
+"\x01\x1A"
+"\x01\x1B"
+"\x01\x1C"
+"\x01\x3D"
+"\x01\x40"
+"\x01\x42"
+"\x01\x43"
+"\x01\x44"
+"\x01\x45"
+"\x01\x4A"
+"\x01\x52"
+"\x01\x53"
+"\x01\x5B"
+"\x02\x12"
+"\x87\x69"
+"\x87\x73"
+"\x88\x25"
+
+# === Compression codes (4-byte LE inline SHORT values) ===
+# These are the values stored in the IFD entry for tag 259
+
+# 1=None 2=Huffman 3=Fax3 4=Fax4 5=LZW
+"\x01\x00\x00\x00"
+"\x02\x00\x00\x00"
+"\x03\x00\x00\x00"
+"\x04\x00\x00\x00"
+"\x05\x00\x00\x00"
+# 6=OldJPEG 7=ModernJPEG 8=Deflate
+"\x06\x00\x00\x00"
+"\x07\x00\x00\x00"
+"\x08\x00\x00\x00"
+# 0x8005=PackBits 0x80B2=OldDeflate
+"\x05\x80\x00\x00"
+"\xB2\x80\x00\x00"
+
+# === Useful small values (4-byte LE) ===
+# BitsPerSample=16, =32 (8 already covered as Deflate compression above)
+
+"\x10\x00\x00\x00"
+"\x20\x00\x00\x00"
+
+# === Minimal IFD entries (12-byte LE: tag + type SHORT + count 1 + value) ===
+# These let the fuzzer splice complete valid entries into an IFD
+
+# ImageWidth=1
+"\x00\x01\x03\x00\x01\x00\x00\x00\x01\x00\x00\x00"
+# ImageLength=1
+"\x01\x01\x03\x00\x01\x00\x00\x00\x01\x00\x00\x00"
+# BitsPerSample=8
+"\x02\x01\x03\x00\x01\x00\x00\x00\x08\x00\x00\x00"
+# Compression=None
+"\x03\x01\x03\x00\x01\x00\x00\x00\x01\x00\x00\x00"
+# PhotometricInterpretation=BlackIsZero
+"\x06\x01\x03\x00\x01\x00\x00\x00\x01\x00\x00\x00"
+# SamplesPerPixel=1
+"\x15\x01\x03\x00\x01\x00\x00\x00\x01\x00\x00\x00"
+# RowsPerStrip=1
+"\x16\x01\x03\x00\x01\x00\x00\x00\x01\x00\x00\x00"