Refactored three large Rust modules (encoding, hash, compression) into focused, modular structures following the pattern established with the base64 module.

Changes

• encoding.rs (1,262 lines) → modular structure with largest file at 517 lines (59% reduction)
• hash.rs (1,036 lines) → modular structure with largest file at 586 lines (43% reduction)
• compression.rs (877 lines) → modular structure with largest file at 296 lines (66% reduction)

Benefits

• Improved maintainability with smaller, focused files
• Tests co-located with implementation
• Clear separation of concerns
• Consistent modular pattern across all large modules

Testing

• All 184 tests passing
• Clippy clean
• Formatted with cargo fmt