BlockId removal: refactor: HeaderBackend::header (#12874)

* BlockId removal: refactor: HeaderBackend::header

It changes the arguments of:
- `HeaderBackend::header`,
- `Client::header`,
- `PeersClient::header`
- `ChainApi::block_header`

methods from: `BlockId<Block>` to: `Block::Hash`

This PR is part of BlockId::Number refactoring analysis (paritytech/substrate#11292)

* non-trivial usages of haeder(block_id) refactored

This may required introduction of dedicated function:
header_for_block_num

* fmt

* fix

* doc fixed

* ".git/.scripts/fmt.sh"

* BlockId removal: refactor: HeaderBackend::expect_header

It changes the arguments of `HeaderBackend::expect_header` method from: `BlockId<Block>` to: `Block::Hash`

* ".git/.scripts/fmt.sh"

* readme updated

* ".git/.scripts/fmt.sh"

* fix

Co-authored-by: parity-processbot <>

substrate/client/service/test/src/client/mod.rs

@@ -1141,13 +1141,22 @@ fn get_block_by_bad_block_hash_returns_none() {
 }
 
 #[test]
-fn get_header_by_block_number_doesnt_panic() {
+fn expect_block_hash_by_block_number_doesnt_panic() {
 	let client = substrate_test_runtime_client::new();
 
 	// backend uses u32 for block numbers, make sure we don't panic when
 	// trying to convert
 	let id = BlockId::<Block>::Number(72340207214430721);
-	client.header(&id).expect_err("invalid block number overflows u32");
+	client.block_hash_from_id(&id).expect_err("invalid block number overflows u32");
+}
+
+#[test]
+fn get_hash_by_block_number_doesnt_panic() {
+	let client = substrate_test_runtime_client::new();
+
+	// backend uses u32 for block numbers, make sure we don't panic when
+	// trying to convert
+	client.hash(72340207214430721).expect_err("invalid block number overflows u32");
 }
 
 #[test]