Add wait_for_ready() to singlecluster route fixture and EnvoyVirtualRoute

> [!NOTE]
> **Missing route waits on multicluster tests routes require additional investigation and issues opened**

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:

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

def wait_for_ready(self):
return
```

**2. Add `wait_for_ready()` to the singlecluster route fixture**

```python
# 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.

Start with testsuite/gateway/envoy/route.py and testsuite/tests/singlecluster/conftest.py, then run the affected singlecluster tests to identify failures caused by waiting after commit(). Done means EnvoyVirtualRoute supports the no-op wait_for_ready(), the singlecluster route fixture calls it, and the triggered test failures are investigated and fixed.

Written by the indexing model from the issue text.