chore(all): review error wrappings

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

internal/configuration/sources/env/helpers.go

@@ -137,7 +137,7 @@ func unsetEnvKeys(envKeys []string, err error) (newErr error) {
 	for _, envKey := range envKeys {
 		unsetErr := os.Unsetenv(envKey)
 		if unsetErr != nil && newErr == nil {
-			newErr = fmt.Errorf("cannot unset environment variable %s: %w", envKey, unsetErr)
+			newErr = fmt.Errorf("unsetting environment variable %s: %w", envKey, unsetErr)
 		}
 	}
 	return newErr