Add fuzzing harnesses for WAV, LAC, block, Rice, and bitstream decoders

[audexdev]

Summary

The parser and decoder surfaces are good fuzzing targets. Add a small fuzzing setup so malformed inputs can be tested continuously and locally.

Proposed targets

• WAV parser: read_wav against arbitrary byte buffers or temporary files
• LAC container decoder: LAC::Decoder::decode
• block decoder: Block::Decoder::decode
• Rice decoder and bitstream reader primitives
• zero-run and bin residual modes

Suggested approach

• Start with libFuzzer-compatible targets under fuzz/.
• Build with ASan/UBSan.
• Add a tiny seed corpus generated from valid synthetic streams.
• Add a CI smoke fuzz mode with a very short runtime.
• Keep longer fuzzing for local/manual runs until runtime is stable.

Acceptance criteria

• Fuzz targets build with CMake.
• At least one LAC decoder and one WAV parser fuzz target can run locally.
• Documentation explains how to run fuzzing and where to place corpus files.