Narrow PR scope to observer tick error isolation; restore synchronous initial render

[Copilot]

This revision removes the previously introduced connectedCallback microtask batching and keeps only the high-value safety fix: a single element error should not abort a dateObserver tick for all observed elements. It also drops per-tick locale/time-zone/hour-cycle caching from this branch to avoid correctness risk and overlap with existing global Intl caching.

• Scope reset: restore main lifecycle semantics

  • Removed module-level pending render queue (pendingElements, pendingFlush, flushPending).
  • Restored synchronous connectedCallback() render (this.update()).
  • Restored disconnectedCallback() and attributeChangedCallback() behavior to match main (no pending-queue coupling).

• Observer robustness: per-element error isolation

  • Guarded each timeEl.update() inside dateObserver.update() so one throw does not stop remaining elements or prevent rescheduling.
  • Preserved global error visibility by rethrowing asynchronously.

• Tests updated to lock intended behavior

  • Removed the full connectedCallback microtask batching suite.
  • Added synchronous-render contract coverage (text/title present immediately after append).
  • Added error-isolation coverage demonstrating other elements continue updating and observer scheduling continues when one element throws.

for (const timeEl of this.elements) {
  nearestDistance = Math.min(nearestDistance, getUnitFactor(timeEl))
  try {
    timeEl.update()
  } catch (error) {
    setTimeout(() => {
      throw error
    })
  }
}