fix cbv route registration on /

[nggit]

When using Class-Based with /:

@app.route('/')
class HelloWorld:
    async def get(self, request):
        return 'GET'

    async def post(self, request):
        return 'POST'

Only the last method or post() is registered. If you do GET, it won't serve the get() but "Method Not Allowed" instead. Like it was not there/not implemented.

/ is really a special case. There is default "Service Unavailable" handler when no route is registered.

But this PR fixes this and with all existing considerations.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud