chore(all): review error wrappings

- remove repetitive `cannot` and `failed` prefixes
- rename `unmarshaling` to `decoding`

internal/storage/servers.go

@@ -28,7 +28,7 @@ func (s *Storage) SetServers(provider string, servers []models.Server) (err erro
 
 	err = s.flushToFile(s.filepath)
 	if err != nil {
-		return fmt.Errorf("cannot save servers to file: %w", err)
+		return fmt.Errorf("saving servers to file: %w", err)
 	}
 	return nil
 }