"""Constructs the metadata URL for a given resource URL following RFC 9728.

This function inserts '/.well-known/oauth-protected-resource' between the host and the path of the resource URL. If the resource URL contains a path, it is appended after the well-known suffix.

Args:
    resource_url (str): The URL of the resource for which the metadata URL is to be constructed.

Returns:
    str: The constructed metadata URL following the RFC 9728 specification.
"""
You should write code starting with:
from urllib.parse import urlunsplit, urlsplit

def metadata_url_for_resource(resource_url: str) -> str:
    # TODO: Implement this function
    pass

