Feature Requests for the Gauge/Speedometer graph

[mmasdivins]

Hello,
First of all thanks for this amazin library.
I've been playing with it and I was trying to create a gauge graph and I found various things I couldn't achieve.

• Center the Gauge: It would be really helpful if the gauge could be centered inside a widget. I have a container with a fixed size and width, and it does not matter what I do that the gauge is drawn on the top left of the widget. Here an example to reproduce:

class Example extends StatelessWidget {
  const Example({super.key});

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(
        title: const Text('Example'),
        backgroundColor: Colors.deepPurple,
        foregroundColor: Colors.white,
      ),
      body: SingleChildScrollView(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.center,
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            SizedBox(
              height: 500,
              width: 800,
              child:
               Center(
                 child:  CristalyseChart()
                   .data([
                     {'metric': 'CPU Usage', 'completion': 35.0, 'type': 'System'},
                   ])
                   .mappingProgress(
                     value: 'completion',
                     label: 'metric',
                     category: 'type',
                   )
                   .geomProgress(
                     orientation: ProgressOrientation.circular,
                     style: ProgressStyle.gauge,
                     thickness: 50,
                     showLabel: true,
                     showTicks: true,
                     fillColor: Colors.green,
                     tickCount: 8,
                     startAngle: -2.356, // -3π/4 (225 degrees)
                     sweepAngle: 4.712, // 3π/2 (270 degrees)
                     gaugeRadius: 80.0, // Required for gauge style
                   )
                   .animate(
                     duration: const Duration(milliseconds: 2000),
                     curve: Curves.elasticOut,
                   )
                   .build(),
               )
            ),

          ],
        ),
      ),
    );
  }
}

• Add label to ticks: I would be helpful if some ticks could have a label, here is an example of what I meant:

- **Adding a gradient to the gauge**: Finally it could also be helpful if we could add a gradient to the gauge in both the fill color and the background color.

Again thanks for this amazing package!