fuzz: add consume_u64

fuzz/fuzz_targets/bitcoin/fuzz_utils.rs

@@ -9,3 +9,25 @@ pub fn consume_random_bytes<'a>(data: &mut &'a [u8]) -> &'a [u8] {
 
     bytes
 }
+
+#[allow(dead_code)]
+pub fn consume_u64(data: &mut &[u8]) -> u64 {
+    // We need at least 8 bytes to read a u64
+    if data.len() < 8 {
+        return 0;
+    }
+
+    let (u64_bytes, rest) = data.split_at(8);
+    *data = rest;
+
+    u64::from_le_bytes([
+        u64_bytes[0],
+        u64_bytes[1],
+        u64_bytes[2],
+        u64_bytes[3],
+        u64_bytes[4],
+        u64_bytes[5],
+        u64_bytes[6],
+        u64_bytes[7],
+    ])
+}