Fix from websockets.(asyncio|sync).router import * without werkzeug

This is a followup for 3128f56

Also, skip test_router_supports_unix_sockets without werkzeug.

Author: hroncok

src/websockets/asyncio/router.py

@@ -35,6 +35,10 @@ def unix_route(
     ) -> Awaitable[Server]:
         raise ImportError("unix_route() requires werkzeug")
 
+    class Router:
+        def __init__(self, *args: Any, **kwargs: Any) -> None:
+            raise ImportError("Router() requires werkzeug")
+
 else:
 
     class Router:

src/websockets/sync/router.py

@@ -35,6 +35,10 @@ def unix_route(
     ) -> Server:
         raise ImportError("unix_route() requires werkzeug")
 
+    class Router:
+        def __init__(self, *args: Any, **kwargs: Any) -> None:
+            raise ImportError("Router() requires werkzeug")
+
 else:
 
     class Router:

tests/asyncio/test_router.py

@@ -186,6 +186,7 @@ async def handler(self, connection):
 
 
 @unittest.skipUnless(hasattr(socket, "AF_UNIX"), "this test requires Unix sockets")
+@unittest.skipUnless("werkzeug" in sys.modules, "werkzeug not installed")
 class UnixRouterTests(EvalShellMixin, unittest.IsolatedAsyncioTestCase):
     async def test_router_supports_unix_sockets(self):
         """Router supports Unix sockets."""