toString method
A string representation of this object.
Some classes have a default textual representation,
often paired with a static parse function (like int.parse).
These classes will provide the textual representation as
their string representation.
Other classes have no meaningful textual representation
that a program will care about.
Such classes will typically override toString to provide
useful information when inspecting the object,
mainly for debugging or logging.
Implementation
@override
String toString() {
  return 'DiagnosticReport(${timestamp.toIso8601String()}, '
      'Model: ${modelType.name}, Format: $originalFormat, '
      'Size: ${originalSizeKB.toStringAsFixed(1)}KB, '
      'Validation: ${validationResult.isValid}, '
      'Base64: $processedBase64Length chars)';
}