- Added constant-time implementations for `PartialEq` and `Eq` using `subtle` crate - Added constant-time implementations for bitwise operations (`XOR`, `AND`, `OR`) in `base_op` - Constant-time operations protect against timing side-channel attacks for cryptographic use cases - Updated README with maintenance-mode notice and feature freeze status - Marked future versions (v0.5.0+) as deprioritized - Removed unused feature flags from crate