* feat: `SliverToolBar`

* chore(example): address lints

* docs(SliverToolbar): update `floating` doc

* feat(example): add page for SliverToolbar

* chore: dart format

* docs(SliverToolBar): slight change to `pinned` docs

* docs(SliverToolBar): add section to readme

* docs(SliverToolBar): tweak sample

* test(SliverAppBar): add initial tests

* chore: update version & changelog

* chore: pub upgrade

* chore: remove unused imports

* test: remove ignore lint