feat: Add Kind::empty_blob() and Kind::empty_tree()`` methods.

Author: Copilot

gix-hash/src/kind.rs

@@ -113,4 +113,16 @@ impl Kind {
             Kind::Sha1 => ObjectId::null_sha1(),
         }
     }
+
+    /// Create an owned empty-blob id of our hash kind.
+    #[inline]
+    pub const fn empty_blob(&self) -> ObjectId {
+        ObjectId::empty_blob(*self)
+    }
+
+    /// Create an owned empty-tree id of our hash kind.
+    #[inline]
+    pub const fn empty_tree(&self) -> ObjectId {
+        ObjectId::empty_tree(*self)
+    }
 }

gix-hash/tests/hash/kind.rs

@@ -14,3 +14,19 @@ mod from_hex_len {
         assert_eq!(Kind::from_hex_len(65), None);
     }
 }
+
+mod empty_objects {
+    use gix_hash::{Kind, ObjectId};
+
+    #[test]
+    fn empty_blob() {
+        let kind = Kind::Sha1;
+        assert_eq!(kind.empty_blob(), ObjectId::empty_blob(kind));
+    }
+
+    #[test]
+    fn empty_tree() {
+        let kind = Kind::Sha1;
+        assert_eq!(kind.empty_tree(), ObjectId::empty_tree(kind));
+    }
+}