python
from google.cloud import bigquery
import datetime
import logging
from flask import Request  # Add type hints for better readability

PROJECT = 'me-gtm-monitoring'  # Update to match your project name
DATASET = 'src_gtm'  # Update to match your dataset name
TABLE = 'raw_data'  # Update to match your table name

# Initialize the BigQuery client globally to avoid re-initialization on each request
client = bigquery.Client()

def stream_bq(uri: str) -> None:
    """
    Streams a single URI to BigQuery.
    
    Args:
        uri (str): The URI to be logged in BigQuery.
    """
    try:
        table_ref = client.dataset(DATASET).table(TABLE)
        #table = client.get_table(table_ref)  # Cache this to avoid unnecessary lookups
    
        # Insert the URI and current timestamp into the table
        rows_to_insert = [{
            'URI': uri, 
            'timestamp': datetime.datetime.utcnow().isoformat()  # Use UTC for consistency
        }]
        errors = client.insert_rows_json(table_ref, rows_to_insert)  # Use insert_rows_json instead of insert_rows

        if errors:  # Log specific errors for better debugging
            logging.error("Errors while inserting rows into BigQuery: %s", errors)
    except Exception as e:
        logging.exception("An unexpected error occurred while streaming to BigQuery: %s", e)


def gtm_monitor(request: Request) -> str:
    """
    Cloud Function entry point. Processes an incoming request and streams the request URL to BigQuery.
    
    Args:
        request (flask.Request): The incoming request object.
    
    Returns:
        str: Response message indicating success or failure.
    """
    try:
        if request and request.url:  # Ensure request object and URL are valid
            logging.info("Received request with URL: %s", request.url)
            stream_bq(request.url)
            return 'Request URL has been successfully streamed to BigQuery.'
        else:
            logging.warning("No URL found in the request.")
            return 'No URL found in the request.'
    except Exception as e:
        logging.exception("An unexpected error occurred in gtm_monitor: %s", e)
        return 'An error occurred while processing the request.'