types: cover split-DNS selectivity for use_with_exit_node

Assert a listed split-domain resolver keeps UseWithExitNode while an
unlisted split resolver in another domain does not, matching the client's
per-resolver useWithExitNodeRoutes filtering.

hscontrol/types/config_test.go

@@ -262,7 +262,8 @@ func TestReadConfig(t *testing.T) {
 					{Addr: "1.0.0.1"},
 				},
 				Routes: map[string][]*dnstype.Resolver{
-					"foo.bar.com": {{Addr: "8.8.8.8", UseWithExitNode: true}},
+					"foo.bar.com":     {{Addr: "8.8.8.8", UseWithExitNode: true}},
+					"baz.example.com": {{Addr: "9.9.9.9"}},
 				},
 			},
 		},

hscontrol/types/testdata/dns-use-with-exit-node.yaml

@@ -21,6 +21,8 @@ dns:
     split:
       foo.bar.com:
         - 8.8.8.8
+      baz.example.com:
+        - 9.9.9.9
     use_with_exit_node:
       - 1.1.1.1
       - 8.8.8.8