PowerSyncDatabaseImpl.connect used to call waitReady() inside of mutex.withLock. That's unfortunate, because initialize also acquires the mutex in updateSchemaInternal. So, when calling connect() immediately after creating a database, there's a potential for a deadlock. The mutex must only be acquired after waiting for the database to be initialized.

To validate the fix, I've migrated the sync tests to stop calling connectInternal and instead use the public connect method. This requires customizing the HTTP client engine passed to the sync engine, for which I've created an (internal) method next to the PowerSyncDatabase factory method.

Closes #169.