webp: Lossless images should use table-based huffman decoder

[fintelia]

The current lossless webp decoding logic does a branch for almost every single bit in the file:

https://github.com/image-rs/image/blob/038bc30b9b9b1daf809452523b557db58f9e781b/src/codecs/webp/huffman.rs#L189-L192

Switching to a more efficient huffman implementation would likely be orders of magnitude faster