Was HEZ-on-Asset-Hub-only. Now data-driven from wallet-utils' new
pezkuwi_assets_for_testBalance.json (TEST_ASSETS_URL), asserting every
asset - HEZ/PEZ/USDT/DOT/ETH/BTC across Pezkuwi's 3 chains - gets an
assets DB row written via a single shared BalancesUpdateSystem run, not
just one asset on one chain. Failure message lists exactly which assets
never synced, by name and chain.