Add wait_for_ready() to singlecluster route fixture and EnvoyVirtualRoute

[averevki]

The default route fixture in testsuite/tests/singlecluster/conftest.py does not call wait_for_ready() after commit(). This was missed when the method was added to HTTPRoute.

Adding the call directly causes some tests to fail and needs investigation.

Changes needed

1. Add no-op wait_for_ready() to EnvoyVirtualRoute

EnvoyVirtualRoute lacks a wait_for_ready() method, so calling it unconditionally on the route fixture would break standalone Authorino tests. Add the following placeholder matching the existing commit()/delete() pattern:

# testsuite/gateway/envoy/route.py
    class HTTPRoute:

    def wait_for_ready(self):
        return

2. Add wait_for_ready() to the singlecluster route fixture

# testsuite/tests/singlecluster/conftest.py
    def route():
    ...
    route.commit()
    route.wait_for_ready()
    return route

3. Investigate and fix test failures triggered by the wait

Some tests fail when the wait is added. These need to be investigated and fixed before merging.