refactor: Unify error boundary for account-info blocking work  #96

One follow-up thought: run_account_info_blocking looks like the right pattern for the other onchain BDK/Electrum blocking calls too, like get_account_info, get_transaction_history, and get_transaction_detail. Could we apply it there in a follow-up so this module has one consistent error boundary for account-info blocking work?

Originally posted by @ben-kaufman in #95 (review)