refactor(core): address the clippy::while_let_on_iterator lint

These loops in `const fn` can now be written as `for` loops.

Author: yvt

src/r3_core/src/bind/sorter.rs

@@ -613,33 +613,22 @@ where
 
     // Calculate `TopologicalSortVertexInfo::num_predecessors`
     let mut num_vertices_remaining = 0;
-    {
-        let mut it_vertices = graph.vertices();
-        while let Some(v) = it_vertices.next() {
-            temp_vertex_info[&v] = TopologicalSortVertexInfo {
-                num_predecessors: 0,
-            };
-            num_vertices_remaining += 1;
-        }
+    for v in graph.vertices() {
+        temp_vertex_info[&v] = TopologicalSortVertexInfo {
+            num_predecessors: 0,
+        };
+        num_vertices_remaining += 1;
     }
-    {
-        let mut it_vertices = graph.vertices();
-        while let Some(v) = it_vertices.next() {
-            let mut it_successors = graph.successors(&v);
-            while let Some(successor) = it_successors.next() {
-                temp_vertex_info[&successor].num_predecessors += 1;
-            }
+    for v in graph.vertices() {
+        for successor in graph.successors(&v) {
+            temp_vertex_info[&successor].num_predecessors += 1;
         }
     }
 
     // Push predecessor-less vertices to `temp_ready_vertex_queue`
-    {
-        let mut it_vertices = graph.vertices();
-        while let Some(v) = it_vertices.next() {
-            if temp_vertex_info[&v].num_predecessors == 0 {
-                temp_ready_vertex_queue
-                    .heap_push(v, ReadyVertexQueueBinaryHeapCtx { vertex_ord_lt });
-            }
+    for v in graph.vertices() {
+        if temp_vertex_info[&v].num_predecessors == 0 {
+            temp_ready_vertex_queue.heap_push(v, ReadyVertexQueueBinaryHeapCtx { vertex_ord_lt });
         }
     }
 
@@ -648,8 +637,7 @@ where
     {
         // Remove `v` from the graph, and push the now-predecessor-less
         // vertices to `temp_ready_vertex_queue`
-        let mut it_successors = graph.successors(&v);
-        while let Some(successor) = it_successors.next() {
+        for successor in graph.successors(&v) {
             temp_vertex_info[&successor].num_predecessors -= 1;
             if temp_vertex_info[&successor].num_predecessors == 0 {
                 temp_ready_vertex_queue