multi.go
func (b *multiLogger) GetLevel(module string) Level {
	var level Level
	for _, backend := range b.backends {
		if backendLevel := backend.GetLevel(module); backendLevel > level {
			level = backendLevel
		}
	}
	return level
}
func (b *multiLogger) GetLevel(module string) Level {
	var level Level
	for _, backend := range b.backends {
		if backendLevel := backend.GetLevel(module); backendLevel > level {
			level = backendLevel
		}
	}
	return level
}
// GetLevel returns the highest level enabled by all backends.