if o < 0 {
					return -1
				}
				i += o + 1
			}
			if s[i+1] == c1 && Equal(s[i:i+n], sep) {
				return i
			}
			fails++
			i++
			// Switch to bytealg.Index when IndexByte produces too many false positives.
			if fails > bytealg.Cutover(i) {
				r := bytealg.Index(s[i:], sep)
				if r >= 0 {
					return r + i
				}
				return -1
			}
		}
		return -1
	}

But `include_router` is still useful to, for example, adding options (like `dependencies`, `prefix`, and `tags`) when including a third party router, or a generic router that is shared between several projects.

This PR allows setting the (mostly new) parameters (additionally to the already existing parameters):

* `default_response_class`: updated to handle defaults in `APIRouter` and `FastAPI`.