feat: add BlockId::as_u64 (alloy-rs#916)

* Add `as_block_number`

* Rename to `as_u64`

* Add tests for `BlockId::as_u64`

* Update crates/eips/src/eip1898.rs

Co-authored-by: Oliver <[email protected]>

---------

Co-authored-by: Oliver <[email protected]>

Author: jmcph4

crates/eips/src/eip1898.rs

@@ -280,6 +280,14 @@ impl BlockId {
         }
     }
 
+    /// Returns the block number if it is [`BlockId::Number`] and not a tag
+    pub const fn as_u64(&self) -> Option<u64> {
+        match self {
+            Self::Number(x) => x.as_number(),
+            _ => None,
+        }
+    }
+
     /// Returns true if this is [BlockNumberOrTag::Latest]
     pub const fn is_latest(&self) -> bool {
         matches!(self, Self::Number(BlockNumberOrTag::Latest))
@@ -750,6 +758,18 @@ mod tests {
         assert_eq!(serialized, "\"0x1\"");
     }
 
+    #[test]
+    fn block_id_as_u64() {
+        assert_eq!(BlockId::number(123).as_u64(), Some(123));
+        assert_eq!(BlockId::number(0).as_u64(), Some(0));
+        assert_eq!(BlockId::earliest().as_u64(), None);
+        assert_eq!(BlockId::latest().as_u64(), None);
+        assert_eq!(BlockId::pending().as_u64(), None);
+        assert_eq!(BlockId::safe().as_u64(), None);
+        assert_eq!(BlockId::hash(BlockHash::ZERO).as_u64(), None);
+        assert_eq!(BlockId::hash_canonical(BlockHash::ZERO).as_u64(), None);
+    }
+
     #[test]
     fn can_parse_eip1898_block_ids() {
         let num = serde_json::json!(