[`MultiHandler`](/pkg/log/slog#MultiHandler) that invokes all the given Handlers.
Its `Enable` method reports whether any of the handlers' `Enabled` methods
return true.
Its `Handle`, `WithAttr` and `WithGroup` methods call the corresponding method

pkg log/slog, method (*MultiHandler) Handle(context.Context, Record) error #65954
pkg log/slog, method (*MultiHandler) WithAttrs([]Attr) Handler #65954
pkg log/slog, method (*MultiHandler) WithGroup(string) Handler #65954