Update Rust structure to better match proposed Python API

src/queue/pure.rs

@@ -1,25 +0,0 @@
-// A "pure" priority queue that supports duplicates, but not arbitrary deletions or weight updates
-use crate::backing::{
-    item::Item,
-    pure::{binary_heap::BinaryHeap, PureBacking},
-};
-use pyo3::prelude::*;
-
-#[pyclass]
-pub struct PureQueue {
-    backing: Box<dyn PureBacking<Item<Py<PyAny>, f64>>>,
-}
-
-#[pymethods]
-impl PureQueue {
-    #[new]
-    fn new() -> Self {
-        Self {
-            backing: Box::new(BinaryHeap::new()),
-        }
-    }
-
-    fn __len__(self_: PyRef<'_, Self>) -> usize {
-        self_.backing.len()
-    }
-}