Stable public release. API is frozen.

Changed #

• Version aligned with the rest of the super_cache family.
• Documentation improvements across all public symbols.

Added #

• SecureCache<K,V> — AES-256-GCM in-memory cache. Each entry is individually encrypted; the nonce and MAC are stored alongside the ciphertext so tampering is detected on get().
• KeyStore abstract interface — inject any key storage backend in tests without a dependency on flutter_secure_storage.
• FlutterSecureKeyStore — production KeyStore backed by flutter_secure_storage. Uses encryptedSharedPreferences: true on Android and the Keychain on iOS/macOS.
• CacheEncryptionConfig — keyAlias and wipeOnEviction options. When wipeOnEviction is true, the intermediate plaintext Uint8List is zeroed out after encryption (best-effort; managed-runtime caveat documented in README).
• SecureCache.initialize() — reads or generates the 256-bit AES key, persists it via KeyStore. Must be called before any get/put.
• Barrel split: super_cache_secure.dart (pure Dart core) and super_cache_secure_flutter.dart (exports FlutterSecureKeyStore).