Merge bitcoindevkit/bdk#634: Get block hash by its height

758dba1 Get block hash by its height (Vladimir Fomene)

Pull request description:

  ### Description
  This PR create a new trait `blockchain::GetBlockHash` with a `get_block_hash` method which returns a block hash given the block height. This has been implemented for all blockchain backends.
  Fixes #603

  ### Notes to the reviewers

  I haven't updated the `CHANGELOG.md` and docs. Am I suppose to update it for this change?

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### New Features:

  * [x] I've added tests for the new feature
  * [ ] I've added docs for the new feature
  * [ ] I've updated `CHANGELOG.md`

ACKs for top commit:
  notmandatory:
    ACK 758dba1

Tree-SHA512: 9c084a6665ecbf27ee8170fdb06e0dc8373d6a901ce29e5f5a1bec111d1507cb3bee6b03a653a55fd20e0fabe7a5eada3353e24a1e21f3a11f01bb9881ae99e5

Author: notmandatory

src/blockchain/esplora/reqwest.rs

@@ -117,6 +117,14 @@ impl GetTx for EsploraBlockchain {
     }
 }
 
+#[maybe_async]
+impl GetBlockHash for EsploraBlockchain {
+    fn get_block_hash(&self, height: u64) -> Result<BlockHash, Error> {
+        let block_header = await_or_block!(self.url_client._get_header(height as u32))?;
+        Ok(block_header.block_hash())
+    }
+}
+
 #[maybe_async]
 impl WalletSync for EsploraBlockchain {
     fn wallet_setup<D: BatchDatabase>(

src/blockchain/esplora/ureq.rs

@@ -112,6 +112,13 @@ impl GetTx for EsploraBlockchain {
     }
 }
 
+impl GetBlockHash for EsploraBlockchain {
+    fn get_block_hash(&self, height: u64) -> Result<BlockHash, Error> {
+        let block_header = self.url_client._get_header(height as u32)?;
+        Ok(block_header.block_hash())
+    }
+}
+
 impl WalletSync for EsploraBlockchain {
     fn wallet_setup<D: BatchDatabase>(
         &self,