Dispute spam protection (#4134)

* Mostly notes.

* Better error messages.

* Introduce Fatal/NonFatal + drop back channel participation

- Fatal/NonFatal - in order to make it easier to use utility functions.
- We drop the back channel in dispute participation as it won't be
needed any more.

* Better error messages.

* Utility function for receiving `CandidateEvent`s.

* Ordering module typechecks.

* cargo fmt

* Prepare spam slots module.

* Implement SpamSlots mechanism.

* Implement queues.

* cargo fmt

* Participation.

* Participation taking shape.

* Finish participation.

* cargo fmt

* Cleanup.

* WIP: Cleanup + Integration.

* Make `RollingSessionWindow` initialized by default.

* Make approval voting typecheck.

* Get rid of lazy_static & fix approval voting tests

* Move `SessionWindowSize` to node primitives.

* Implement dispute coordinator initialization.

* cargo fmt

* Make queues return error instead of boolean.

* Initialized: WIP

* Introduce chain api for getting finalized block.

* Fix ordering to only prune candidates on finalized events.

* Pruning of old sessions in spam slots.

* New import logic.

* Make everything typecheck.

* Fix warnings.

* Get rid of obsolete dispute-participation.

* Fixes.

* Add back accidentelly deleted Cargo.lock

* Deliver disputes in an ordered fashion.

* Add module docs for errors

* Use type synonym.

* hidden docs.

* Fix overseer tests.

* Ordering provider taking `CandidateReceipt`.

... To be kicked on one next commit.

* Fix ordering to use relay_parent

as included block is not unique per candidate.

* Add comment in ordering.rs.

* Take care of duplicate entries in queues.

* Better spam slots.

* Review remarks + docs.

* Fix db tests.

* Participation tests.

* Also scrape votes on first leaf for good measure.

* Make tests typecheck.

* Spelling.

* Only participate in actual disputes, not on every import.

* Don't account backing votes to spam slots.

* Fix more tests.

* Don't participate if we don't have keys.

* Fix tests, typos and warnings.

* Fix merge error.

* Spelling fixes.

* Add missing docs.

* Queue tests.

* More tests.

* Add metrics + don't short circuit import.

* Basic test for ordering provider.

* Import fix.

* Remove dead link.

* One more dead link.

Co-authored-by: Lldenaurois <Ljdenaurois@gmail.com>