In previous implementations object size limiter left checksums of parent
object payload unset. This was caused by the closure that written calculated
checksums to the child object instead of parent one.
Construct payload checksum writers in separate function in order to prevent
closure bug.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Define object writer interface. Implement payload size limiter that
restricts payload size of the object. Implement object format moulder that
fill verification fields and finalizes object structure.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
