test: add unit tests for handler, logger, manager, and config
Cover Handler property accessors, format delegation, emit contract,
and close lifecycle. Cover Logger level methods, isEnabledFor caching,
manager property assignment, handler management, debug invocation,
and makeRecord extra key collision. Cover Manager getLogger hierarchy
setup, placeholder fixup, disable level, and loggerClass validation.
Cover basicConfig option handling, force flag, mutual exclusion of
stream/filename/handlers, and formatter assignment.
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