Db suggestions

[tamirms]

1. The NORMAL synchronous mode is recommended while using WAL, see https://sqlite.org/pragma.html#pragma_synchronous
2. I discovered there is a common interface for testing.T and testing.B which can be used to simplify creating test dbs https://pkg.go.dev/testing#TB
3. It is not necessary to commit a read only transaction so we can reduce boilerplate by doing a defer tx.rollback on read functions. For the updater, it seems like we should always rollback on errors because I don't think we will continue to use the updater after encountering an error.

[2opremio]

About the updater, I was only rolling back on database errors (or that was the intention). If the error is not related to the DB, it could be retried.

[tamirms]

If the error is not related to the DB, it could be retried.

I think the non db errors are encoding / decoding errors:

	encodedKey, err := encodeLedgerKey(l.buffer, key)
	if err != nil {
		return err
	}
	// safe since we cast to string right away
	encodedEntry, err := l.buffer.UnsafeMarshalBinary(&entry)
	if err != nil {
		return err
	}

so if you retry I don't think the error will go away.