WAL file grows to 2GiB during Sepolia testnet class definitions sync phase of checkpoint sync

[kkovaacs]

Looks like we're keeping a read transaction (in ExpectedDeclarations::spawn()) open for the whole duration of the class definitions sync. This causes SQLite to be unable to merge WAL records back into the DB and causes the WAL file to grow to 2 GiB during the class definitions sync phase.