Update disputes prioritisation in `dispute-coordinator` (#6130)

* Scraper processes CandidateBacked events

* Change definition of best-effort

* Fix `dispute-coordinator` tests

* Unit test for dispute filtering

* Clarification comment

* Add tests

* Fix logic

If a dispute is not backed, not included and not confirmed we
don't participate but we do import votes.

* Add metrics for refrained participations

* Revert "Add tests"

This reverts commit 7b8391a087922ced942cde9cd2b50ff3f633efc0.

* Revert "Unit test for dispute filtering"

This reverts commit 92ba5fe678214ab360306313a33c781338e600a0.

* fix dispute-coordinator tests

* Fix scraping

* new tests

* Small fixes in guide

* Apply suggestions from code review

Co-authored-by: Andrei Sandu <54316454+sandreim@users.noreply.github.com>

* Fix some comments and remove a pointless test

* Code review feedback

* Clarification comment in tests

* Some tests

* Reference counted `CandidateHash` in scraper

* Proper handling for Backed and Included candidates in scraper

Backed candidates which are not included should be kept for a
predetermined window of finalized blocks. E.g. if a candidate is backed
but not included in block 2, and the window size is 2, the same
candidate should be cleaned after block 4 is finalized.

Add reference counting for candidates in scraper. A candidate can be
added on multiple block heights so we have to make sure we don't clean
it prematurely from the scraper.

Add tests.

* Update comments in tests

* Guide update

* Fix cleanup logic for `backed_candidates_by_block_number`

* Simplify cleanup

* Make spellcheck happy

* Update tests

* Extract candidate backing logic in separate struct

* Code review feedback

* Treat  backed and included candidates in the same fashion

* Update some comments

* Small improvements in test

* spell check

* Fix some more comments

* clean -> prune

* Code review feedback

* Reword comment

* spelling

Co-authored-by: Andrei Sandu <54316454+sandreim@users.noreply.github.com>