chore(all): review error wrappings

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

internal/openvpn/extract/data.go

@@ -17,12 +17,12 @@ func (e *Extractor) Data(filepath string) (lines []string,
 	connection models.Connection, err error) {
 	lines, err = readCustomConfigLines(filepath)
 	if err != nil {
-		return nil, connection, fmt.Errorf("cannot read configuration file: %w", err)
+		return nil, connection, fmt.Errorf("reading configuration file: %w", err)
 	}
 
 	connection, err = extractDataFromLines(lines)
 	if err != nil {
-		return nil, connection, fmt.Errorf("cannot extract connection from file: %w", err)
+		return nil, connection, fmt.Errorf("extracting connection from file: %w", err)
 	}
 
 	return lines, connection, nil