Zombienet tests - disputes on finalized blocks (#2184)

**Overview:**
Adding an extra malus variant focusing on disputing finalized blocks. It
will:
- wrap around approval-voting
- listen to `OverseerSignal::BlockFinalized` and when encountered start
a dispute for the `dispute_offset`th ancestor
- simply pass through all other messages and signals

Add zombienet tests testing various edgecases:
- disputing freshly finalized blocks
- disputing stale finalized blocks
- disputing eagerly pruned finalized blocks (might be separate PR)

**TODO:**
- [x] Register new malus variant
- [x] Simple pass through wrapper (approval-voting)
- [x] Simple network definition
- [x] Listen to block finalizations
- [x] Fetch ancestor hash
- [x] Fetch session index
- [x] Fetch candidate
- [x] Construct and send dispute message
- [x] zndsl test 1 checking that disputes on fresh finalizations resolve
valid Closes #1365
- [x] zndsl test 2 checking that disputes for too old finalized blocks
are not possible Closes #1364
- [ ] zndsl test 3 checking that disputes for candidates with eagerly
pruned relay parent state are handled correctly #1359 (deferred to a
separate PR)
- [x] Unit tests for new malus variant (testing cli etc)
- [x] Clean/streamline error handling
- [ ] ~~Ensure it tests properly on session boundaries~~

---------

Co-authored-by: Javier Viola <javier@parity.io>
Co-authored-by: Marcin S. <marcin@realemail.net>
Co-authored-by: Tsvetomir Dimitrov <tsvetomir@parity.io>

polkadot/node/malus/src/variants/common.rs

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
-//! Implements common code for nemesis. Currently, only `FakeValidationResult`
+//! Implements common code for nemesis. Currently, only `ReplaceValidationResult`
 //! interceptor is implemented.
 use crate::{
 	interceptor::*,
@@ -188,7 +188,7 @@ where
 		let _candidate_descriptor = candidate_descriptor.clone();
 		let mut subsystem_sender = subsystem_sender.clone();
 		let (sender, receiver) = std::sync::mpsc::channel();
-		self.spawner.spawn_blocking(
+		self.spawner.spawn(
 			"malus-get-validation-data",
 			Some("malus"),
 			Box::pin(async move {