Unify REP and EC code in GET server implementation #3760
Description
This duplicates some logic we already have in the service (assembly_v2.go) which will add maintenance cost and headache. We need more code reuse for split assembly.
Originally posted by @roman-khimov in #3754 (comment)
code is quite outdated, and many updates have been added on top of it, only adding to its complexity. The EC was the largest, so it was added nearby. It is proposed to perform a general code refactoring in careful, small steps. The secondary goal is to share the common logic between REP and EC.