Parse and Summarise Log Files

When something breaks in production, you're often grepping logs. Write a parser that summarises them.

Each well-formed line looks like:

2024-05-01 10:00:01 ERROR [db] connection refused

That's a date, a time, a level (DEBUG, INFO, WARNING or ERROR), a service name in square brackets (letters, digits, _, . or -), then the message.

Implement parse_logs(lines) returning a dict:

• "levels": count of lines per level (only levels that appear)
• "errors_by_service": count of ERROR lines per service
• "error_messages": ERROR messages in order
• "skipped": number of lines that don't match the format, including blank lines

Lines may end with "\n".