Keep a scan out of route-proxy's unrouted state: only names under a served domain, a few a minute, no visitor address (issue 774)

Review of ddae6729: a scanner's random Host or SNI names each became a key, bounded only by the
bucket's lifetime and size, and every failed write was retried at each change and logged each time.

A refused name is now kept by name only under the registrable domain of a name the proxy serves, and
at most five new names a minute; every other refusal is counted in memory and written once a minute
under <node>._other (last minute, since start), which route_proxy_unrouted shows. A refused write of
that state is dropped and logged once until a write succeeds; trimming memory to 4096 names moved
from the request to the writer. The visitor's address is no longer kept: the journal has it.

Quick: drop unrouted keys from strangers by a fixed allow-list. Thorough: bound by the proxy's own
domains, by rate, and by never retrying. Chose thorough: the scan is constant on a public machine.

modules/route-proxy/cmd/route-provider/tools_test.go

@@ -52,6 +52,7 @@ func TestTheWebFrontsToolsAnswerFromTheBus(t *testing.T) {
 	unrouted := held{
 		"anchor.old.example":  routestate.Unrouted{Name: "old.example", Proxy: "anchor", AskedAt: now.Add(-time.Hour), Times: 3},
 		"anchor.wiki.example": routestate.Unrouted{Name: "wiki.example", Proxy: "anchor", AskedAt: now, Times: 1},
+		"anchor._other":       routestate.Other{Proxy: "anchor", Minute: now, LastMinute: 40, SinceStart: 900},
 	}
 	tools := map[string]stdio.Tool{}
 	for _, tool := range (front{routes: routes, unrouted: unrouted, now: func() time.Time { return now }}).tools() {
@@ -72,7 +73,8 @@ func TestTheWebFrontsToolsAnswerFromTheBus(t *testing.T) {
 		{RouteTool, map[string]any{"name": "wiki.example"}, []string{`"routed":false`,
 			`answered \"no route\" for it, last at 2026-10-30T21:00:00Z`}},
 		{RouteTool, map[string]any{"name": "nothing.example"}, []string{`"routed":false`, `none was asked for it`}},
-		{UnroutedTool, nil, []string{`"names":2`, `"unrouted":[{"name":"wiki.example"`}},
+		{UnroutedTool, nil, []string{`"names":2`, `"unrouted":[{"name":"wiki.example"`,
+			`"other_refusals":[{"proxy":"anchor"`, `"last_minute":40`, `"since_start":900`}},
 	} {
 		t.Run(row.tool, func(t *testing.T) {
 			tool, ok := tools[row.tool]