Should clone record before calling .Add on it for the Go "slog" integration

[cideM]

I noticed that the Go integration for slog does not call rec.Clone() before adding to the record. The documentation for slog states:

Sometimes a Handler will need to modify a Record before passing it on to another Handler or backend. A Record contains a mixture of simple public fields (e.g. Time, Level, Message) and hidden fields that refer to state (such as attributes) indirectly. This means that modifying a simple copy of a Record (e.g. by calling Record.Add or Record.AddAttrs to add attributes) may have unexpected effects on the original. Before modifying a Record, use Record.Clone to create a copy that shares no state with the original, or create a new Record with NewRecord and build up its Attrs by traversing the old ones with Record.Attrs.

[felixge]

Thanks for spotting and reporting this 🙇. #2929 should fix it.