fix: unused clippy warning

Author: yannham

libdd-trace-utils/src/span/vec_map.rs

@@ -10,7 +10,7 @@
 
 use serde::ser::{Serialize, Serializer};
 use std::borrow::Borrow;
-use std::collections::{HashMap, HashSet};
+use std::collections::HashSet;
 use std::hash::Hash;
 
 /// A Vec-backed map that provides HashMap-like lookup by key.