PoA warp implementation (#5488)

* separate modules for consensus snapshot chunks

* bulk of authority warp logic

* finish authority warp implementation

* squash warnings and enable authority snapshot mode

* test harness for PoA

* fiddle with harness

* epoch generation proof fixes

* update constructor code

* store epoch transition proof after block commit

* basic snap and restore test

* use keyvaluedb in state restoration

* decompress chunks

* fix encoding issues

* fixed-to-contract-to-contract test

* implement ancient block import

* restore genesis transition in PoW snapshot

* add format version method to snapshot components

* supported version numbers in snapshot_components

* allow returning of ancient epoch transitions

* genesis hash mismatch check

* remove commented code

sync/src/tests/snapshot.rs

@@ -71,6 +71,10 @@ impl SnapshotService for TestSnapshotService {
 		self.manifest.as_ref().cloned()
 	}
 
+	fn min_supported_version(&self) -> Option<u64> {
+		Some(1)
+	}
+
 	fn chunk(&self, hash: H256) -> Option<Bytes> {
 		self.chunks.get(&hash).cloned()
 	}