performance: icedisk_rel_table is slow

[adsharma]

lbug -i xet://datasets/ladybugdb/ldbc-csr/main/cit-Patents-csr/schema.cypher
lbug> profile match (a)-[b]->(c) return a.id, c.id limit 10;
...

is rather slow.

Probably inefficiencies in ice_disk_rel_table.{cpp,h} on how the scan works.
Also potentially screwing up the join order due to the lack of tablestats.

Suggested debug strategy: download the dataset locally, profile the pread system calls using bpfcc-tools.

[adsharma]

Cc: @rahul21-7 this may be a good one to look into

[rahul21-7]

okay, I'll look into it, thank you

[adsharma]

This is probably not a good first issue. Removing the label.