A more comprehensive model for PoV-Blocks and Candidate receipts (#843)

* encode the candidate statement as only the hash

* refactor CandidateReceipt and CollationInfo

* introduce an abridged candidate receipt type

* erasure coding stores candidate receipt

* store omitted data instead and introduce AvailableData type

* refactor availability-store schema

* tweak schema and APIs a bit more

* get availability-store tests passing

* accept AbridgedCandidateReceipt in `set_heads`

* change statement type in primitives to be hash-only

* fix parachains runtime tests

* fix bad merge

* rewrite validation pipeline

* remove evaluation module

* use abridged candidate hash as canonical

* statement table uses abridged candidate receipts

* kill availability_store::Data struct

* port shared table to new validation pipelines

* extract full validation pipeline to helper

* remove old validation pipeline from collation module

* polkadot-validation compiles

* polkadot-validation tests compile

* make local collation available in validation service

* port legacy network code

* polkadot-network fully ported

* network: ensure fresh statement is propagated

* remove pov_block_hash from LocalValidationData

* remove candidate_hash field from AttestedCandidate and update runtime

* port runtimes to new ParachainHost definition

* port over polkadot-collator

* fix test compilation

* better fix

* remove unrelated validation work dispatch fix

* address grumbles

* fix equality check

polkadot/parachain/src/wasm_executor/mod.rs

@@ -79,7 +79,7 @@ pub enum Error {
 	#[display(fmt = "IO error: {}", _0)]
 	Io(std::io::Error),
 	#[display(fmt = "System error: {}", _0)]
-	System(Box<dyn std::error::Error>),
+	System(Box<dyn std::error::Error + Send>),
 	#[display(fmt = "WASM worker error: {}", _0)]
 	External(String),
 	#[display(fmt = "Shared memory error: {}", _0)]
@@ -129,10 +129,14 @@ pub fn validate_candidate<E: Externalities + 'static>(
 		},
 		#[cfg(target_os = "unknown")]
 		ExecutionMode::Remote =>
-			Err(Error::System("Remote validator not available".to_string().into())),
+			Err(Error::System(Box::<dyn std::error::Error + Send + Sync>::from(
+				"Remote validator not available".to_string()
+			) as Box<_>)),
 		#[cfg(target_os = "unknown")]
 		ExecutionMode::RemoteTest =>
-			Err(Error::System("Remote validator not available".to_string().into())),
+			Err(Error::System(Box::<dyn std::error::Error + Send + Sync>::from(
+				"Remote validator not available".to_string()
+			) as Box<_>)),
 	}
 }