Prevent component destruction to support bfcache

[nikrom17]

Summary

Enable bfcache (Back/Forward Cache) support by preventing component destruction when the page is entering bfcache.

Browsers fire pagehide with event.persisted = true when a page enters bfcache, and pageshow with event.persisted = true when restored. Previously, zoid treated every pagehide as a real navigation and
destroyed components — making them non-functional on bfcache restore.

Changes

Parent (src/parent/parent.js):

• Remove once() wrapper on the pagehide listener so it can fire on every bfcache cycle
• Add event.persisted guard — skip destroy() when the page is entering bfcache, only destroy on real navigation
• Add logging to watchElementForClose callback to trace rerender vs close paths

Child (src/child/child.js):

• Add event.persisted guard on the pagehide listener — skip checkClose signal when the page is entering bfcache

Component (src/component/component.js):

• Add logging to the rerender() path for debugging bfcache restore behavior

How it works

Event	persisted	Behavior
pagehide	true	Page entering bfcache — skip destroy/checkClose, components survive
pagehide	false/undefined	Real navigation — destroy components as before
pageshow	true	Page restored from bfcache — components are still alive

Related PRs

• Depends on: belter watchElementForClose bfcache fix (prevents sacrificial iframe from triggering false-positive rerender on bfcache restore)
• Prior work: Conditionally add unload event listener (enable bfcache) #475 (conditionally add unload event listener)

Test plan

• Load page with zoid components → navigate away → browser back button → components survive without re-render
• Real navigation (close tab, navigate to external URL) → components destroy normally
• Existing test suite passes (test/tests/error.js dispatches new Event("pagehide") with persisted=undefined, which is falsy — guard does not skip it)