* add assumptions made by the Node-side

* Update roadmap/implementers-guide/src/node/README.md

Co-authored-by: Peter Goodspeed-Niklaus <[email protected]>

* Update roadmap/implementers-guide/src/node/README.md

Co-authored-by: Peter Goodspeed-Niklaus <[email protected]>

* Update roadmap/implementers-guide/src/node/README.md

Co-authored-by: Bernhard Schuster <[email protected]>

* more refinements

Co-authored-by: Peter Goodspeed-Niklaus <[email protected]>
Co-authored-by: Bernhard Schuster <[email protected]>

Per https://github.com/paritytech/polkadot/commit/69ce9ff#r40392855

* Updates guide for CandidateBacking

* Move assignment types to primitives

* Initial implementation.

* More functionality

* use assert_matches

* Changes to report misbehaviors

* Some fixes after a review

* Remove a blank line

* Update guide and some types

* Adds run_job function

* Some comments and refactorings

* Fix review

* Remove warnings

* Use summary in kicking off validation

* Parallelize requests

* Validation provides local and global validation params

* Test issued validity tracking

* Nits from review

* introduce candidatedescriptor type

* add PoVDistribution message type

* loosen bound on PoV Distribution to account for equivocations

* re-export some types from the messages module

* begin PoV Distribution subsystem

* remove redundant index from PoV distribution

* define state machine for pov distribution

* handle overseer signals

* set up control flow

* remove `ValidatorStatement` section

* implement PoV fetching

* implement distribution logic

* add missing `

* implement some network bridge event handlers

* stub for message processing, handle our view change

* control flow for handling messages

* handle `awaiting` message

* handle any incoming PoVs and redistribute

* actually provide a subsystem implementation

* remove set-builder notation

* begin testing PoV distribution

* test that we send awaiting messages only to peers with same view

* ensure we distribute awaited PoVs to peers on view changes

* test that peers can complete fetch and are rewarded

* test some reporting logic

* ensure peer is reported for flooding

* test punishing peers diverging from awaited protocol

* test that we eagerly complete peers' awaited PoVs based on what we receive

* test that we prune the awaited set after receiving

* expand pov-distribution in guide to match a change I made

* remove unneeded import

* rename implementor's guide to implementer's guide

* fix typos in more places