Limit number of headers that are pruned within single import Call (#105)

* removeInMemoryStorage + extract Kovan stuff to runtime

* removed comment from the future

* limit number of headers that are pruned within single import Call

* verify that pruning range upper bottom is always-increasing

* Fix typo

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

bridges/modules/ethereum/src/import.rs

@@ -171,7 +171,7 @@ mod tests {
 		validator, validators, validators_addresses, TestRuntime,
 	};
 	use crate::validators::ValidatorsSource;
-	use crate::{BridgeStorage, Headers, OldestUnprunedBlock};
+	use crate::{BlocksToPrune, BridgeStorage, Headers, PruningRange};
 	use frame_support::{StorageMap, StorageValue};
 
 	#[test]
@@ -264,7 +264,7 @@ mod tests {
 	}
 
 	#[test]
-	fn headers_are_pruned() {
+	fn headers_are_pruned_during_import() {
 		custom_test_ext(genesis(), validators_addresses(3)).execute_with(|| {
 			let validators_config =
 				ValidatorsConfiguration::Single(ValidatorsSource::Contract([3; 20].into(), validators_addresses(3)));
@@ -354,7 +354,13 @@ mod tests {
 				latest_block_hash = rolling_last_block_hash;
 				step += 3;
 			}
-			assert_eq!(OldestUnprunedBlock::get(), 11);
+			assert_eq!(
+				BlocksToPrune::get(),
+				PruningRange {
+					oldest_unpruned_block: 11,
+					oldest_block_to_keep: 14,
+				},
+			);
 
 			// now let's insert block signed by validator 1
 			// => blocks 11..24 are finalized and blocks 11..14 are pruned
@@ -380,7 +386,13 @@ mod tests {
 			)
 			.unwrap();
 			assert_eq!(finalized_blocks, expected_blocks);
-			assert_eq!(OldestUnprunedBlock::get(), 15);
+			assert_eq!(
+				BlocksToPrune::get(),
+				PruningRange {
+					oldest_unpruned_block: 15,
+					oldest_block_to_keep: 15,
+				},
+			);
 		});
 	}
 }