verify: add verify_pattern_interval option

verify: add verify_pattern_interval option

It can be useful to fill a device by writing each LBA with its offset
using a verify_pattern value that includes the %o format specifier.
However, it is slow to do this 512B at a time for a large device. This
patch adds the verify_pattern_interval option to enable fio to write
such a data pattern using larger transfer sizes. With this option set,
fio will update the offset every verify_pattern_interval bytes. For a
4096-byte block with verify_pattern=%o the first 512 bytes will be 0,
the second 512 bytes will be 512, the third 512 bytes will be 1024, etc
when verify_pattern_interval=512.

When verify_pattern does not include %o the verify_pattern_interval
option will still re-start the verify pattern eveny N bytes.

Link: https://lore.kernel.org/r/20250508185832.3702-9-vincent.fu@samsung.com
Signed-off-by: Vincent Fu <vincent.fu@samsung.com>