Add url normalization for list of URLs

[OnSuorce]

This PR is related to issue #545 and #556 .

Changes

Extracted the normalization logic into a new method which is then called to both normalize URL s from a single string and multiple string from a List.

def _normalize_url(self, url: str):
        """
        Normalizes and validates a connection URL to ensure compatibility.
        Adds default schemes and ports if missing, and checks for a valid hostname.
        """
        try:
            if "nats://" in url or "tls://" in url:
                # Closer to how the Go client handles this.
                # e.g. nats://localhost:4222
                uri = urlparse(url)
            elif "ws://" in url or "wss://" in url:
                uri = urlparse(url)
            elif ":" in url:
                # Expand the scheme for the user
                # e.g. localhost:4222
                uri = urlparse(f"nats://{url}")
            else:
                # Just use the endpoint with the default NATS port.
                # e.g. demo.nats.io
                uri = urlparse(f"nats://{url}:4222")

            # In case only endpoint with scheme was set.
            # e.g. nats://demo.nats.io or localhost:
            # the ws and wss do not need a default port as the transport will assume 80 and 443, respectively
            if uri.port is None and uri.scheme not in ("ws", "wss"):
                # Set default NATS port 4222 if no port is specified
                uri = urlparse(f"nats://{uri.hostname}:4222")

            if uri.hostname is None or uri.hostname == "none":
                # Validates the hostname
                raise errors.Error("nats: invalid hostname in connect url")

            return uri
        except ValueError:
            raise errors.Error("nats: invalid connect url option")

Added simple check to split a string containing ","

if isinstance(connect_url, str) and "," in connect_url:
            connect_url = connect_url.strip().split(",")

Added tests to check new syntax even though they are not annotated to be actually tested