Three bookkeeping import bugs found by reading other projects' sample files

ai-bookkeeper reads bank files from dozens of banks, but most of its tests use rows we wrote ourselves. A cheap way to find real faults is to feed it sample files that other open-source projects keep for their own importers. Today's sweep covered 4 QFX and 17 QIF files from GnuCash and the CSV fixtures of Paisa.

Three faults came out:

• ICICI credit-card CSV. Amounts are unsigned and a separate BillingAmountSign column says CR for a credit. We ignored it, so every card charge was booked as money in, and 01/03/2023 was read as January 3 instead of March 1. The header Amount(in Rs) was not recognised either.
• Quicken dates after 1999. Old QIF files write 29 March 2000 as 3/29' 0. Those rows were dropped: one sample imported 2 of 7 transactions.
• Category and class lists. QIF files list categories before the transactions. They were read as transactions and produced a page of "unreadable date" warnings that hid real problems.

All three are fixed with tests. The ICICI fix is checked only against a one-sided sample (charges, no CR rows), so a real statement with credits is still wanted.