_find_best_variant now searches by hash (md5, sha1, crc32, sha256)
across the entire database instead of only by filename. Finds
variants stored under different names (e.g. eu_mcd2_9306.bin for
bios_CD_E.bin, scph1001_v20.bin for scph1001.bin).
verify_entry_existence now also calls _find_best_variant to
suppress discrepancies when a matching variant exists in the repo.
Reduces false discrepancies from 22 to 11 (4 unique files where
the variant genuinely does not exist in the repo).
28ecf19f2b