我需要经常在stable和master频道之间切换，以使用一些新功能或能够运行某些项目（例如flutter / gallery）。
并且每次我运行命令flutter channel master / stable后跟flutter upgrade时，似乎都在下载新的Dart SDK，其中包含许多其他内容（请参见下面的输出） ），因此切换并不轻松，我不得不等待，即使频道之间的时间只有几秒钟！
> flutter channel stable
Switching to flutter channel 'stable'...
git: Your branch is up to date with 'origin/stable'.
git: Switched to branch 'stable'
Successfully switched to flutter channel 'stable'.
To ensure that you're on the latest build from this channel, run 'flutter upgrade'
PS D:\DevLib\Flutter\flutter_course> flutter doctor
Checking Dart SDK version...
Downloading Dart SDK from Flutter engine 6bc433c6b6b5b98dcf4cc11aff31cdee90849f32...
Unzipping Dart SDK...
Building flutter tool...
Running pub upgrade...
╔════════════════════════════════════════════════════════════════════════════╗
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╚════════════════════════════════════════════════════════════════════════════╝
Downloading package sky_engine... 1.6s
Downloading flutter_patched_sdk tools... 6.4s
Downloading flutter_patched_sdk_product tools... 6.4s
Downloading windows-x64 tools... 14.9s
Downloading windows-x64/font-subset tools... 2.3s
Downloading android-arm-release/windows-x64 tools... 1.5s
Downloading android-arm64-profile/windows-x64 tools... 1.9s
Downloading android-arm64-release/windows-x64 tools... 1.5s
Downloading android-x64-profile/windows-x64 tools... 1.9s
Downloading android-x64-release/windows-x64 tools... 1.7s
Doctor summary (to see all details, run flutter doctor -v):