Error recovery: no retry path once an observable cache entry errors

## Problem

Once a reactfire hook enters `status: 'error'`, there is no way to recover without remounting with a different `observableId`.

The errored `SuspenseSubject` stays in the global `preloadedObservables` cache under its `observableId`. On error, the 30-second reset timer is cancelled (it becomes a no-op timeout), and the observable does not re-subscribe. A component that remounts with the same `observableId` rejoins the same errored subject and immediately receives `status: 'error'` again.

This became user-visible in v4.3.0, which made `status: 'error'` reachable in non-suspense mode (previously errors always threw, so the stuck state was hidden). Users building `status === 'error'` UI now have no way to trigger a retry.

## Current workaround

Change the `observableId` passed to the hook. This causes `preloadObservable` to create a fresh `SuspenseSubject` and re-subscribe to the source. Not a real API — just an escape hatch.

## What a fix might look like

- An explicit `retry()` / `reset()` function returned from the hook, or
- A `retryOnError` option that re-subscribes automatically after a delay, or
- Cache eviction on error after the reset timeout (restoring the pre-v4.3 behavior for the cache entry, not for error surfacing)

The right shape is an open question. Filing to track the gap.

Closes none. Related to #735.

Start at preloadObservable and the global preloadedObservables cache, then trace SuspenseSubject error and reset behavior through the hook's non-suspense status path. Done means an agreed retry or reset path lets an errored entry recover with the same observableId, without requiring a different ID or remount workaround.

索引モデルが issue の本文から書いたものです。