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/web/src/lib.rs

@@ -27,7 +27,7 @@ use tracing::info;
 
 pub use api::{
     AttrSummary, ConfigView, LocalRouteView, PeerView, ReceivedRouteView, RefusalsView,
-    RefusedRouteView, RpkiView, StatusView,
+    RefusedRouteView, RoutesPage, RpkiView, StatusView,
 };
 
 /// Static facts about the router shown in status output.