Protect against out of band writes to sqlite

[gorbak25]

Circumventing the corrosion API and inserting data directly into the sqlite db is not supported. Such OOB writes are not replicated to other nodes. When corrosion encounters OOB mutations it will think it missed some messages from other nodes, create an entry in the __corro_bookkeeping_gaps table and wait forever for the missing db_version.

To prevent accidental OOB writes I suggest modifying https://github.com/superfly/cr-sqlite to reject all writes unless the ENABLE_WRITES pragma on the connection is enabled. This way people attempting OOB inserts will get notified that those changes won't be synced by corrosion.