Make sure we properly wrap all errors

Using %w instead of %v makes Errorf store the original error, allowing the caller to extract and use it later. While there isn’t any immediate benefit from it, it may be useful in future.

See:

• https://go.dev/doc/go1.13#error_wrapping
• https://github.com/golang/go/wiki/ErrorValueFAQ
• https://go.googlesource.com/proposal/+/master/design/29934-error-values.md