Dispute Coordinator Subsystem (#3150)

* skeleton for dispute-coordinator

* add coordinator and participation message types

* begin dispute-coordinator DB

* functions for loading

* implement strongly-typed DB transaction

* add some tests for DB transaction

* core logic for pruning

* guide: update candidate-votes key for coordinator

* update candidate-votes key

* use big-endian encoding for session, and implement upper bound generator

* finish implementing pruning

* add a test for note_current_session

* define state of the subsystem itself

* barebones subsystem definition

* control flow

* more control flow

* implement session-updating logic

* trace

* control flow for message handling

* Update node/core/dispute-coordinator/src/lib.rs

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* Update node/subsystem/src/messages.rs

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* some more control flow

* guide: remove overlay

* more control flow

* implement some DB getters

* make progress on importing statements

* add SignedDisputeStatement struct

* move ApprovalVote to shared primitives

* add a signing-payload API to explicit dispute statements

* add signing-payload to CompactStatement

* add relay-parent hash to seconded/valid dispute variatns

* correct import

* type-safe wrapper around dispute statements

* use checked dispute statement in message type

* extract rolling session window cache to subsystem-util

* extract session window tests

* approval-voting: use rolling session info cache

* reduce dispute window to match runtime in practice

* add byzantine_threshold and supermajority_threshold utilities to primitives

* integrate rolling session window

* Add PartialOrd to CandidateHash

* add Ord to CandidateHash

* implement active dispute update

* add dispute messages to AllMessages

* add dispute stubs to overseer

* inform dispute participation to participate

* implement issue_local_statement

* implement `determine_undisputed_chain`

* fix warnings

* test harness for dispute coordinator tests

* add more helpers to test harness

* add some more helpers

* some tests for dispute coordinator

* ignore wrong validator indices

* test finality voting rule constraint

* add more tests

* add variants to network bridge

* fix test compilation

* remove most dispute coordinator functionality

as of #3222 we can do most of the work within the approval voting subsystem

* Revert "remove most dispute coordinator functionality"

This reverts commit 9cd615e8eb6ca0b382cbaff525d813e753d6004e.

* Use thiserror

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* Update node/core/dispute-coordinator/src/lib.rs

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* extract tests to separate module

* address nit

* adjust run_iteration API

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>
Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

polkadot/node/core/approval-voting/src/tests.rs

@@ -191,7 +191,7 @@ impl DBReader for TestStore {
 
 fn blank_state() -> State<TestStore> {
 	State {
-		session_window: import::RollingSessionWindow::default(),
+		session_window: RollingSessionWindow::new(APPROVAL_SESSIONS),
 		keystore: Arc::new(LocalKeystore::in_memory()),
 		slot_duration_millis: SLOT_DURATION_MILLIS,
 		db: TestStore::default(),
@@ -204,10 +204,11 @@ fn single_session_state(index: SessionIndex, info: SessionInfo)
 	-> State<TestStore>
 {
 	State {
-		session_window: import::RollingSessionWindow {
-			earliest_session: Some(index),
-			session_info: vec![info],
-		},
+		session_window: RollingSessionWindow::with_session_info(
+			APPROVAL_SESSIONS,
+			index,
+			vec![info],
+		),
 		..blank_state()
 	}
 }
@@ -231,7 +232,7 @@ fn sign_approval(
 	candidate_hash: CandidateHash,
 	session_index: SessionIndex,
 ) -> ValidatorSignature {
-	key.sign(&super::approval_signing_payload(ApprovalVote(candidate_hash), session_index)).into()
+	key.sign(&ApprovalVote(candidate_hash).signing_payload(session_index)).into()
 }
 
 #[derive(Clone)]