[#87976] Reduce error flash to avoid cookie overflows

This originally addressed cookie overflow in order imports, but in the mean time we found that the cookie overflow avoidance code in journal creation wasn't always working. 5781cfe should make cookie overflow with journaling errors a lot less likely, but there's more we could do, like not repeating the same message when several order details fail for the same reason.
I wonder how important the order detail # is here. If we could get rid of it we could run `uniq` over `row_errors`.