"""Extracts the file extension from a given URI.

The function parses the URI to extract the path component and then identifies the file extension
by splitting the path on the '.' character. If a '.' is found in the path, the function returns
the extension in lowercase, prefixed with a '.'. If no '.' is found, an empty string is returned.

Args:
    uri (str): The URI from which to extract the file extension.

Returns:
    str: The file extension in lowercase, prefixed with a '.', or an empty string if no extension is found.
"""