Logging Framework

Design a logging library like a simplified version of Python's logging or Log4j: callers log messages at levels, and the framework filters, formats, and writes them to one or more destinations. It tests pattern fluency (Chain of Responsibility, Strategy, Singleton) and non-blocking I/O thinking.

Requirements

Functional

• Log levels: DEBUG < INFO < WARN < ERROR < FATAL; each logger has a minimum level.
• logger.info("msg", **context) creates a record with timestamp, level, logger name, message, and context.
• Multiple sinks (appenders): console, file, remote HTTP endpoint; each sink can have its own level and formatter.
• Pluggable formatters: plain text, JSON.
• Named, hierarchical loggers (app.payments inherits config from app).
• Configuration at startup (code or dict).

Non-functional

• Logging must never crash the application, and should add minimal latency to the caller.
• Thread-safe: many threads log concurrently without interleaved lines.
• Ordering preserved per sink.
• Extensible: new sinks and formatters without modifying core classes.