Assorted Cache API fixes

[mrbbot]

Each of these fixes is split into a separate commit for easier reviewing. 🙂

• Enable persistence: previously the cachePersist option was being ignored, so cached data couldn't be persisted
• Disable Workers Sites asset caching: we always want to serve the latest on-disk Workers Sites files so changes are reflected. However, @cloudlfare/kv-asset-handler automatically caches files, so we need to disable the Cache API for these URIs.
• Allow cache to be disabled: Miniflare 2 had a cache: false option for disabling the cache. The Cache API was still available, it just didn't do anything.
• Facilitate cache usage warning on workers.dev subdomains: Cache API operations are no-ops on workers.dev subdomains. This is a common cause of confusion, so this PR also brings over Miniflare 2's cacheWarnUsage: true option. We can set this in Wrangler if we detect the user will be publishing to a workers.dev zone.

[changeset-bot]

⚠️ No Changeset found

Latest commit: ad80536

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[penalosa]

Lgtm 🎉