Availability store pruning (#1820)

* Initial commit

* Move tests to separate module

* Move timestamps to the newtype

* Change idx name

* Use Duration for consts and update chunk records

* Ordering::Equal

* Update node/core/av-store/src/lib.rs

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* put_ methods do the array sorting

* Fix get_block_number

* Change StoreChunk message type and relay parent method

* Add chunk tests

* Fix block number computation for StoreChunk

* Duration instead of u64 everywhere

* Add a clarifying comment

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

polkadot/node/network/availability-distribution/src/lib.rs

@@ -661,6 +661,7 @@ where
 					if let Err(_e) = store_chunk(
 						ctx,
 						message.candidate_hash.clone(),
+						live_candidate.descriptor.relay_parent.clone(),
 						message.erasure_chunk.index,
 						message.erasure_chunk.clone(),
 					).await? {
@@ -949,6 +950,7 @@ where
 async fn store_chunk<Context>(
 	ctx: &mut Context,
 	candidate_hash: Hash,
+	relay_parent: Hash,
 	validator_index: ValidatorIndex,
 	erasure_chunk: ErasureChunk,
 ) -> Result<std::result::Result<(), ()>>
@@ -957,7 +959,13 @@ where
 {
 	let (tx, rx) = oneshot::channel();
 	ctx.send_message(AllMessages::AvailabilityStore(
-		AvailabilityStoreMessage::StoreChunk(candidate_hash, validator_index, erasure_chunk, tx),
+		AvailabilityStoreMessage::StoreChunk {
+			candidate_hash,
+			relay_parent,
+			validator_index,
+			chunk: erasure_chunk,
+			tx,
+		}
 	)).await?;
 	rx.await.map_err::<Error, _>(Into::into)
 }