"""Transform commits from a single repository into user-repository relationships.

This function processes a list of commits from a single GitHub repository and transforms them into a list of user-repository relationship records. It is optimized for memory efficiency by processing one repository at a time. The function skips commits where the author's user URL is not available.

Args:
    repo_name (str): The name of the repository.
    commits (list[dict[str, Any]]): A list of commit data from the repository. Each commit is a dictionary containing details such as the author and commit date.
    organization (str): The name of the GitHub organization.

Returns:
    list[dict[str, Any]]: A list of user-repository relationship records. Each record contains the user URL, repository URL, commit count, and the first and last commit dates.
"""
You should write code starting with:
from datetime import datetime
from typing import Any, List, Dict

def transform_single_repo_commits_to_relationships(
    repo_name: str,
    commits: List[Dict[str, Any]],
    organization: str,
) -> List[Dict[str, Any]]:
    # TODO: Implement this function
    pass

