ioutil.ReadAll is deprecated since Go1.16 - see https://tip.golang.org/doc/go1.16#ioutil
VictoriaMetrics requires at least Go1.18, so it is OK to switch from ioutil.ReadAll to io.ReadAll.
This is a follow-up for 02ca2342ab
due to memory align the metaindexRow structure use 64-byte pre object.
this commit changes the order of field, make metaindexRow use 56-byte pre
object.
Signed-off-by: Sasasu <su@sasasu.me>