v1.2.0 of cachemesh

Result-first caching and data orchestration layer for Dart and Flutter apps. Memory-first cache with policies, single-flight dedup, and reactive watch streams. Changelog excerpt: Persistence & offline support — no breaking changes. - Pluggable disk persistence: new PersistentStoreasync interface plus two implementations — InMemoryPersistentStore(tests/demos) and JsonFileStore(file-backed, dart:io). JsonFileStorelives in a separate entry point, package:cachemesh/cachemesh_io.dart, so the core library stays web-compatible. Bring your own backend (Hive, sqflite, shared_preferences) by implementing PersistentStore. - Typed serialization: register a `Ca[...]