Fix crash on Incoming Message class

[AbhijeetMallick]

Problem:
On devices where the SQLite message store fails to initialize, the app falls back to an in-memory store. When MQTTCourierClient.destroy() attempts to delete pending messages using NSBatchDeleteRequest, it crashes with NSInternalInconsistencyException: "Unknown command type ". This is because NSBatch*Request is only supported on SQLite stores, not in-memory stores.

Solution:
Added useSafeDeleteForNonSQLiteStore flag (defaults to true) to IncomingMessagePersistence
Track which store type was actually initialized (resolvedStoreType)
Route deletion based on store type:
SQLite store → use fast NSBatchDeleteRequest (unchanged)
In-memory store → use safe fetch-and-delete loop (works on all store types)
Flag can be set to false to revert to old behavior if needed