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() {
  final textContent = text;
  final calls = toolCalls;
  final thinkingContent = thinking;
  final parts = <String>[];
  if (thinkingContent != null) {
    parts.add('Thinking: $thinkingContent');
  }
  if (calls != null) {
    parts.add(calls.map((c) => c.toString()).join('\n'));
  }
  if (textContent != null) {
    parts.add(textContent);
  }
  return parts.join('\n');
}