不知何故，所有小部件都被重建

Question

问题

所有小部件都可以通过单击按钮进行重建。
我只想重建按钮小部件。

使用单个按钮小部件并不是主要的性能问题，但是随着按钮小部件数量的增加，性能会急剧下降。
仅用一个按钮，性能就不足30fps。

环境

Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel master, v1.15.17-pre.5, on Microsoft Windows [Version 10.0.18362.657], locale ja-JP)

[√] Android toolchain - develop for Android devices (Android SDK version 29.0.0)
[√] Chrome - develop for the web
[√] Android Studio (version 3.6)
[√] VS Code (version 1.42.1)
[√] Connected device (4 available)

• No issues found!

代码

import 'package:flutter/material.dart';

void main() => runApp(Home());

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
          body: SafeArea(
            child: Center(
              child: DurationButton(),
            )
          )
      )
    );
  }
}


class DurationButton extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    final Size size = MediaQuery.of(context).size;
    return SizedBox(
      height: size.width/3.75,
      width: size.width/3.75,
      child: RaisedButton(
        elevation: 10.0,
        onPressed: () {},
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            const Spacer(flex: 15,),
            Text(
              "PREPARE",
              style: Theme.of(context).textTheme.bodyText2,
              textAlign: TextAlign.center,
            ),
            const Spacer(flex: 10),
            const Text('20s'),
            const Spacer(flex: 15,),
          ],
        ),
        shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(10.0)
        ),
      ),
    );
  }
}