[w3c/ServiceWorker] Editorial: use a per-cache dedicated parallel queue for Cache API methods (PR #1843)

Closes #1841. Follow-up to #1755, sibling to #1838.

Give each [=request response list=] (the internal representation of a {{Cache}} object) a dedicated parallel queue and route the {{Cache}} methods that read or mutate it through the queue, so reads and writes on the same {{Cache}} object are serialized.

## Changes

- Add `<dfn>request response list parallel queue</dfn>` (a [=parallel queue=]) attached to each [=request response list=], following the same pattern that #1838 introduced for the [=name to cache map=].
- Route the following {{Cache}} method algorithms through it, replacing their existing `Run … in parallel` block:
    - {{Cache/matchAll(request, options)}}
    - {{Cache/addAll(requests)}} — only the batch-commit step; the per-request fetch step is left as bare `in parallel` since it does not touch the [=request response list=].
    - {{Cache/put(request, response)}}
    - {{Cache/delete(request, options)}}
    - {{Cache/keys(request, options)}}
- The existing `Queue a task` wrappers around promise resolution / rejection (from #1837) are preserved inside the enqueued steps.

Total change: **+7 / −5** in `index.bs`, one commit.

## Out of scope (deliberately)

- {{Cache/match(request, options)}} — a pure orchestrator that delegates to `matchAll`; enqueueing it too would cause a deadlock (it waits on a promise that can only be settled by another enqueued step). Covered transitively.
- {{Cache/add(request)}} — pure orchestrator that delegates to `addAll`. Same reason.
- {{Cache/addAll}}'s per-request fetch block — only performs [=/fetching=]; does not touch the [=request response list=].

## Rationale

Yoshi flagged this concern during #1755 review:

> The situation should also be the same for the [=cache=] object. I guess each [=cache=] object will have the dedicated parallel queue, and `match()`, `matchAll()`, `add()`, `addAll()`, `put()`, `delete()`, and `keys()` might also executed within the parallel queue for the [=cache=] object.

#1837 landed the queue-a-task-for-resolve fixes for these methods. This PR delivers the sibling per-cache parallel-queue work that was explicitly deferred in the [split plan](https://github.com/w3c/ServiceWorker/pull/1755#issuecomment-4963401716).

## Coordination

The changes here do not overlap textually with the queue-a-task changes in #1837 — that PR only touches the promise resolve/reject lines, this PR only touches the outer `Run in parallel` lines. Either can merge first.

## Related

- #1755 — parent (queue-a-task refactor)
- #1837 — Cache API queue-a-task-for-resolve (open)
- #1838 — sibling PR (CacheStorage `name to cache map` parallel queue), same dfn pattern
- #1740 — original missing-tasks-in-parallel issue
- #1831 — cache/cache-storage forgot to queue a task to resolve promise
- #1172 — umbrella "Carefully audit all uses of 'in parallel' in the spec"
- #1842 — sibling PR (Clients API parallel queue), same dfn pattern


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You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/ServiceWorker/pull/1843

-- Commit Summary --

  * Editorial: use a per-cache dedicated parallel queue for Cache API methods

-- File Changes --

    M index.bs (12)

-- Patch Links --

https://github.com/w3c/ServiceWorker/pull/1843.patch
https://github.com/w3c/ServiceWorker/pull/1843.diff

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