Write a function to optimize a log processing task for memory efficiency. Implement process_logs(log_lines) using a single pass over an iterable of log strings. Each line begins with one level, INFO, WARNING, ERROR, or DEBUG, followed by a space and message; return counts for all four levels. For example, ["INFO Started", "ERROR Failed"] returns { "INFO": 1, "WARNING": 0, "ERROR": 1, "DEBUG": 0 }, while an empty iterable returns zero counts.
def process_logs(log_lines):