rproxy tests: give the 1 MiB answer a 60 s time limit (closes #335)

Test only. `TestAnAnswerOf1MiBGoesToTheVisitor` read an answer of 1 MiB from `waf` within the default `SWRP_TIMEOUT_MS` of 2 s. On a busy host that time ran out first, `rproxy` applied `SWRP_DEFAULT_DISPOSITION` as it should, and the test failed. It now sets `SWRP_TIMEOUT_MS` to `60000`, as the file's other tests do where that limit is not what they test.

Model: opus-5-5

internal/rproxy/rproxy_test.go

@@ -1023,7 +1023,9 @@ func TestAnAnswerOf1MiBGoesToTheVisitor(t *testing.T) {
 		w.WriteHeader(http.StatusInternalServerError)
 		_, _ = w.Write(make([]byte, size))
 	})
-	addr, _ := startRProxy(t, standIn.URL, nowhere, nil)
+	addr, _ := startRProxy(t, standIn.URL, nowhere, map[string]string{
+		timeoutSetting: "60000",
+	})
 
 	got := get(t, addr, "/")
 	if got.status != http.StatusInternalServerError || len(got.body) != size {