fix: race condition in transaction

[DominicGBauer]

Problem

We were sporadically encountering IllegalStateException with the message "Transaction objects must be used only within the transaction lambda scope." This typically indicates a race condition where transaction objects are being accessed across different threads or coroutine contexts. I initially thought it was because of a transaction in BucketStorageImpl was using the wrong context (which was addressed in this PR #89) but this was not the case as the issue persisted.

Root Cause

Database operations were not consistently running on the same dispatcher, which could lead to transaction objects being accessed from different threads. SQLDelight requires transaction operations to maintain thread confinement for safety.

Solution

Added a dedicated IO dispatcher for all database operations by modifying the database driver creation:

val dbDispatcher = Dispatchers.IO
val dbScope = CoroutineScope(scope.coroutineContext + dbDispatcher)

This will also improve DB operation performance as the operations are now always running on the correct dispatcher.

Testing

Testing in the Swift demo no longer produces this error (although it's tough to say that this is definitively resolved since the error was sporadic).