AFF4: leitura (snappy/deflate/LZ4, mapas esparsos) e gravação; CLI --format aff4

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

scripts/fetch-testdata.sh

@@ -16,4 +16,8 @@ mkdir -p "$dest/dfvfs"
 for f in lvm.raw apfs.raw apfs_encrypted.dmg hfsplus.raw hfs.raw xfs.raw xfs-bigtime.raw ext4.raw ext2.raw fvdetest.qcow2 luks1.raw luks2.raw bdetogo.raw; do
   [ -f "$dest/dfvfs/$f" ] || curl -fsSL "https://raw.githubusercontent.com/log2timeline/dfvfs/main/test_data/$f" -o "$dest/dfvfs/$f"
 done
+mkdir -p "$dest/aff4"
+for f in Base-Linear.aff4 Base-Allocated.aff4 Base-Linear-AllHashes.aff4; do
+  [ -f "$dest/aff4/$f" ] || curl -fsSL "https://raw.githubusercontent.com/aff4/ReferenceImages/master/AFF4Std/$f" -o "$dest/aff4/$f"
+done
 echo "ok: $dest"