IsCode is a convenience wrapper for `errors.Is` `errors.Is(err, "foo")` does not work `IsCode(err, "foo")` does - as the string is automatically converted.

Merrer (merr-er) represents a merr-compatible error It primarily exists to allow `Wrap` to return nil without forcing us to use pointers for `E`, but also allows other structs to offer a merr.E option.

nolint:errname // package name is already error-scoped.