[Blockchain]block_propose_command_handler refac

[ttkmw]

Component
Blockchain

Assignee
anyone who wanna do

Problem or Necessity
there is an issue that handling ProposedCommand

For now, it just check sync is processing or not.
But when blockchain is shorter than block pool's first staged block,
it'll be good if we synchronize then save staged blocks.

The case is just a little error case, so it is not big problem

we can fix it later

Detail
write here

Reference
write here