block: rename tuple_size field in blk_integrity to metadata_size

block: rename tuple_size field in blk_integrity to metadata_size

The tuple_size field in blk_integrity currently represents the total
size of metadata associated with each data interval. To make the meaning
more explicit, rename tuple_size to metadata_size. This is a purely
mechanical rename with no functional changes.

Suggested-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
Link: https://lore.kernel.org/20250630090548.3317-2-anuj20.g@samsung.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>