Update Rust structure to better match proposed Python API

src/backing/indexed/mod.rs

@@ -0,0 +1,12 @@
+/// Data structures for the "indexed" min-queues, supporting priority updates and arbitrary removals, but no duplicates
+use super::{item::Item, pure::PureBacking};
+
+/// A data structure usable for backing an "indexed" queue
+pub trait IndexedBacking<D: Clone + Send + Sync, P: Ord + Clone + Send + Sync>:
+    PureBacking<Item<D, P>>
+{
+    /// Update an item's priority
+    fn update(data: D, priority: P) -> Result<(), ()>;
+    /// Remove an item from the queue
+    fn remove(data: D) -> bool;
+}