[FINAL] Adding an endpoint to fetch bitcoin block headers

spec/_attachments/ic.did

@@ -76,12 +76,14 @@ type bitcoin_network = variant {
 
 type bitcoin_address = text;
 
-type block_hash = blob;
+type bitcoin_block_hash = blob;
 
 type bitcoin_block_header = blob;
 
 type millisatoshi_per_byte = nat64;
 
+type bitcoin_block_height = nat32;
+
 type outpoint = record {
     txid : blob;
     vout : nat32;
@@ -104,8 +106,8 @@ type bitcoin_get_utxos_args = record {
 
 type bitcoin_get_utxos_result = record {
     utxos : vec utxo;
-    tip_block_hash : block_hash;
-    tip_height : nat32;
+    tip_block_hash : bitcoin_block_hash;
+    tip_height : bitcoin_block_height;
     next_page : opt blob;
 };
 
@@ -120,8 +122,8 @@ type bitcoin_get_utxos_query_args = record {
 
 type bitcoin_get_utxos_query_result = record {
     utxos : vec utxo;
-    tip_block_hash : block_hash;
-    tip_height : nat32;
+    tip_block_hash : bitcoin_block_hash;
+    tip_height : bitcoin_block_height;
     next_page : opt blob;
 };
 
@@ -153,13 +155,13 @@ type bitcoin_send_transaction_args = record {
 };
 
 type bitcoin_get_block_headers_args = record {
-	start_height : nat32;
-	end_height : opt nat32;
+    start_height : bitcoin_block_height;
+    end_height : opt bitcoin_block_height;
 };
 
 type bitcoin_get_block_headers_result = record {
-	tip_height : nat32;
-	block_headers : vec bitcoin_block_header;
+    tip_height : bitcoin_block_height;
+    block_headers : vec bitcoin_block_header;
 };
 
 type node_metrics = record {

spec/index.md

@@ -2378,6 +2378,12 @@ The [standard nearest-rank estimation method](https://en.wikipedia.org/wiki/Perc
 
 ### IC method `bitcoin_get_block_headers` {#ic-bitcoin_get_block_headers}
 
+:::note
+
+The node metrics management canister API is considered EXPERIMENTAL. Canister developers must be aware that the API may evolve in a non-backward-compatible way.
+
+:::
+
 Given a start height and an optional end height, the function returns the block headers in the provided range. The range is inclusive, i.e., the block headers at the start and end heights are returned as well.
 
  If no end height is specified, all blocks until the tip height, i.e., the largest available height, are returned. However, if the range from the start height to the end height or the tip height is large, only a prefix of the requested block headers may be returned in order to bound the size of the response.