单页面生命周期PageVisibilityObserver，没有效果。

flutter_boost版本是v3.0-null-safety-preview.10，
使用方法是按照文档中的写的。
@override
void onPageShow() {
super.onPageShow();
print("pagelife-onPageShow");
}

@override
void onPageHide() {
super.onPageHide();
print("pagelife-onPageHide");
}

@override
void onForeground() {
super.onForeground();
print("pagelife-onForeground");
}

@override
void onBackground() {
super.onBackground();
print("pagelife-onBackground");
}
问题是：没有打印信息

Start with PageVisibilityObserver and the four overridden callbacks shown in the report, using flutter_boost v3.0-null-safety-preview.10 and the documented usage. Reproduce the page lifecycle and app foreground/background transitions, then trace why none of the callbacks print; done means the expected callbacks fire in the relevant transitions.

Written by the indexing model from the issue text.