v0.20.1

A patch of fixes: the Lit tab in Firefox DevTools works again after opening
blank since 0.19.0, server-rendered elements hydrate with the source overlay
on, and closing a panel tab always clears what it drew. Nothing needs action
to upgrade.

Fixed

• The Lit tab works in Firefox DevTools again. Since 0.19.0 it opened
  blank in Firefox; it now shows the site's status and the inspector once the
  site is enabled.
• Server-rendered Lit elements hydrate with the source overlay on. An
  element whose template renders another custom element no longer re-renders
  in the browser with a warning about an edit that never happened, in Astro or
  any other server rendering.
• Closing a panel tab always clears what it drew on the page. The anatomy
  overlay, outline and Live mode no longer outlive a panel tab that closed too
  fast to say so, or crashed.
• The panel stops filling the console with warnings. Opening it no longer
  prints Web Awesome's size="small" is deprecated warnings, and a panel in a
  tab of its own, at /__lit/ or in Firefox's DevTools, no longer warns that
  the in-page channel has no handshake targets.