Page through the received routes, on the status page and in the API

/api/routes/received now returns one page: {routes, next_after,
prev_before}. Pages are in prefix order and begin at a prefix (after= or
before=), not at a count, so a table that changes between two pages does
not make them overlap or leave a gap. A page holds whole prefixes, about
`limit` routes' worth.

The table keeps prefixes in no order, so a page is found by looking at
every prefix once and keeping the nearest few; the routes of the others
are not touched (RibTable::for_each_prefix).

The status page shows about 100 routes with first / previous / next
links; the place is kept in the page's address with the lookup.

The response of /api/routes/received was an array before: this changes
its shape.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/integration-tests/tests/http_api.rs

@@ -169,7 +169,8 @@ async fn test_received_routes_summary() -> Result<()> {
 
     let received = tokio::time::timeout(TIMEOUT, async {
         loop {
-            let v = get_json(&client, &format!("{base}/api/routes/received")).await?;
+            let v =
+                get_json(&client, &format!("{base}/api/routes/received")).await?["routes"].take();
             if !v.as_array().unwrap().is_empty() {
                 return Ok::<_, eyre::Error>(v);
             }