Image struct (always RGBA8) with conversions from grayscale,
grayscale+alpha, RGB, RGBA, indexed color, and indexed+alpha.
29 unit tests covering all conversion paths and edge cases.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Parse zlib header (CMF/FLG), validate header checksum, delegate to
DEFLATE for compressed data, verify Adler-32 checksum of output.

21 unit tests covering Adler-32, header validation, round-trip
decompression, error propagation, and all window sizes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Pure Rust DEFLATE decompression supporting all three block types:

- Non-compressed blocks (BTYPE=00) with LEN/NLEN validation
- Fixed Huffman codes (BTYPE=01) per RFC 1951 §3.2.6
- Dynamic Huffman codes (BTYPE=10) with code length decoding

Implementation details:
- LSB-first bit reader with peek/consume pattern for Huffman decoding
- Two-level Huffman lookup table (primary + subtable for long codes)
- LZ77 back-reference decoding with overlapping copy support
- Handles end-of-stream gracefully when final code needs fewer bits
than the primary table width

33 unit tests covering BitReader, Huffman trees, all block types,
back-references, error cases, and round-trip verification against
zlib-generated test vectors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>