Address PR review feedback:
- Remove benches/decode.rs which referenced non-existent gen_bench_tiff.c
- Simplify compute_tiff_hash: replace 66-line match block with
as_buffer().as_bytes() + ByteOrder::convert for LE normalization
- Use TIFF Type repr(u16) as hash discriminant instead of ad-hoc u8
- Rename all 74 seq test images to match updated hashes
Measures decode throughput for 1024x1024 gray images at various bit
depths (3-24 bit). Requires pre-generated images in /tmp/bench-tiff/
(see stderr instructions for generation).