请使用flutter设计一个用于显示曲线图的chart控件，支持手势缩放，有坐标轴显示，右上角显示曲线编号及对应颜色，支持空安全；有可传递曲线数据的增加曲线函数，新增曲线随机使用不同的颜色；有清空曲线函数；使用charts_flutter库；可设置坐标轴参数

以下是一个使用charts_flutter库实现的简单的可缩放曲线图控件，支持手势缩放、坐标轴显示、曲线编号及对应颜色显示、空安全、新增曲线及清空曲线功能。代码中有注释说明如何使用和设置坐标轴参数。

import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;

class ZoomableChart extends StatefulWidget {
  ZoomableChart({Key? key}) : super(key: key);

  @override
  _ZoomableChartState createState() => _ZoomableChartState();
}

class _ZoomableChartState extends State<ZoomableChart> {
  final List<List<charts.Series<TimeSeriesData, DateTime>>> _seriesList = [];
  final List<String> _seriesNames = [];
  final List<Color> _seriesColors = [];

  // 控制手势缩放的控制器
  final _zoomController = charts.ChartController();

  // 控制曲线条数的计数器
  int _seriesCount = 0;

  // 添加一条新曲线
  void addSeries(List<TimeSeriesData> data) {
    final seriesName = 'Series $_seriesCount';
    final seriesColor = Color((Math.Random().nextDouble() * 0xFFFFFF).toInt()).withOpacity(1.0);
    final series = _createSeries(data, seriesName, seriesColor);
    setState(() {
      _seriesList.add(series);
      _seriesNames.add(seriesName);
      _seriesColors.add(seriesColor);
      _seriesCount++;
    });
  }

  // 清空所有曲线
  void clear() {
    setState(() {
      _seriesList.clear();
      _seriesNames.clear();
      _seriesColors.clear();
      _seriesCount = 0;
    });
  }

  // 创建曲线
  List<charts.Series<TimeSeriesData, DateTime>> _createSeries(
      List<TimeSeriesData> data, String seriesName, Color seriesColor) {
    return [
      charts.Series<TimeSeriesData, DateTime>(
        id: seriesName,
        colorFn: (_, __) => charts.ColorUtil.fromDartColor(seriesColor),
        domainFn: (TimeSeriesData data, _) => data.time,
        measureFn: (TimeSeriesData data, _) => data.value,
        data: data,
      )
    ];
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Zoomable Chart'),
      ),
      body: Column(
        children: [
          // 曲线图
          Expanded(
            child: charts.TimeSeriesChart(
              _seriesList.isNotEmpty ? _seriesList[0] : [],
              animate: false,
              dateTimeFactory: const charts.LocalDateTimeFactory(),
              behaviors: [
                // 手势缩放
                charts.PanAndZoomBehavior(
                  panningCompletedCallback: () {},
                  zoomingCompletedCallback: () {},
                  maxScaleFactor: 20,
                  minScaleFactor: 0.5,
                  selectionModelTrigger: charts.SelectionModelTrigger.none,
                  chartController: _zoomController,
                ),
              ],
              primaryMeasureAxis: charts.NumericAxisSpec(
                tickProviderSpec: charts.BasicNumericTickProviderSpec(zeroBound: false),
                renderSpec: charts.GridlineRendererSpec(
                  labelStyle: charts.TextStyleSpec(
                    fontSize: 12,
                    color: charts.MaterialPalette.gray.shadeDefault,
                  ),
                  lineStyle: charts.LineStyleSpec(
                    color: charts.MaterialPalette.gray.shade300,
                  ),
                ),
              ),
              domainAxis: charts.DateTimeAxisSpec(
                tickFormatterSpec: charts.AutoDateTimeTickFormatterSpec(
                  day: charts.TimeFormatterSpec(
                    format: 'd',
                    transitionFormat: 'MM/dd',
                  ),
                ),
                renderSpec: charts.GridlineRendererSpec(
                  labelStyle: charts.TextStyleSpec(
                    fontSize: 12,
                    color: charts.MaterialPalette.gray.shadeDefault,
                  ),
                  lineStyle: charts.LineStyleSpec(
                    color: charts.MaterialPalette.gray.shade300,
                  ),
                ),
              ),
            ),
          ),
          // 曲线编号及对应颜色
          SizedBox(
            height: 40,
            child: ListView.builder(
              scrollDirection: Axis.horizontal,
              itemCount: _seriesNames.length,
              itemBuilder: (context, index) {
                return Row(
                  children: [
                    SizedBox(width: 8),
                    Container(
                      width: 20,
                      height: 20,
                      color: _seriesColors[index],
                    ),
                    SizedBox(width: 4),
                    Text(_seriesNames[index]),
                    SizedBox(width: 8),
                  ],
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}

// 时间序列数据
class TimeSeriesData {
  final DateTime time;
  final double value;

  TimeSeriesData(this.time, this.value);
}