fs: make FILE_EXTENT_SAME failures self-describing

fs: make FILE_EXTENT_SAME failures self-describing

The old error dumped the raw btrfs_ioctl_same_args struct after the
source path.  With long backup-snapshot pathnames the line was
truncated before the destination offset, so the log rarely contained
enough to understand or reproduce the failure.

Emit the parameters of dedupe_file_range directly: the src file and
offset, the length, and every dst file and offset.  That is the full
set of inputs needed to replay the ioctl by hand.

Assisted-by: Claude-Code:claude-opus-4-7
Signed-off-by: Zygo Blaxell <bees@furryterror.org>