Unified secure storage with built-in encryption and pluggable backends Changelog excerpt: ### Added - `SecureStore`with encrypted read/write for strings, JSON, bools, and ints - `StorageBackend`abstract interface for pluggable backends - `MemoryBackend`for in-memory storage (testing and development) - `FileBackend`for JSON file-based persistent storage - `Encryption`with salt-based XOR and key-derived PRNG - `readOrThrow`for strict key access - `allKeys`, `containsKey`, `delete`, `clear`operations - Zero external dependencies