feat(apr): Implement LZ4/ZSTD decompression for compressed APR v2 files

[noahgift]

Summary

Add decompression support for APR v2 files with LZ4 or ZSTD compression flags.

Current State

• AprFlags::LZ4_COMPRESSED and AprFlags::ZSTD_COMPRESSED flags are defined
• Loading compressed files returns error: "Compressed .apr files not yet supported"

Implementation

• Add lz4_flex and zstd dependencies (feature-gated)
• Implement decompression in AprModel::from_bytes()
• Syncs with aprender GH-146 compression support

Benefit

• Smaller model files for deployment
• Faster network transfer
• Consistent with aprender's APR format compression