codec: migrate to scale

[dshulyak]

Use https://github.com/spacemeshos/go-scale in the codec module.

before working on this issue implement https://github.com/spacemeshos/go-scale/issues/2

Using scale for majority of the objects should be trivial:

• add go generate with scalegen
• for every collection define sensible limit using tag name defined above
• add a fuzz tests and a golden tests (you should be able to find utilities for both in the lib above)

If some objects uses collections with pointers in them - they should be replaced with collections without pointers.

There is also some mess with types from poet/post, but i don't recall details.

Modules to enable scale codec for:

• [x] transactions - https://github.com/spacemeshos/go-spacemesh/pull/3380
• [x] blocks - https://github.com/spacemeshos/go-spacemesh/pull/3377
• [x] ballots - https://github.com/spacemeshos/go-spacemesh/pull/3383
• [x] proposals - https://github.com/spacemeshos/go-spacemesh/pull/3383
• [ ] poet proofs
• [ ] sync