WebP VP8L Implementation Notes

• Status: complex Huffman coding implemented; LZ77 backward references and color cache not implemented. Current encoder produces valid VP8L streams for Huffman-only encodings; full compression requires LZ77 & color cache.
• Decoder: VP8L (lossless) decoder with fault-tolerant mode (enabled by default) for pixel-level error recovery. Fills remaining pixels with gray when Huffman/LZ77 decoding fails.
• Decoder/Encoder files: src/formats/webp.ts, src/utils/webp_encoder.ts, src/utils/webp_decoder.ts.
• Tests: test/formats/webp.test.ts, test/formats/webp_tolerant.test.ts, test/purejs_roundtrip.test.ts.
• Notes: implemented: canonical Huffman generation, code-length RLE, and writing of all required Huffman groups (green, red, blue, alpha, distance). Fault-tolerant decoding allows partial recovery from corrupted VP8L images. Remaining work: implement LZ77 match finding & encoding, and color cache to reach full lossless compression parity with libwebp.