feat: add cloudflare kv adapter

[connorads]

What?

Add a Cloudflare KV adapter to extend recent KV support (#9913)
Discussion: #14431

👋 I'm very open to comments and feedback

Why?

So that Cloudflare users can use Cloudflare KV as a backing store for Payload’s KV API.

How?

• Implement a @payloadcms/kv-cloudflare package that satisfies the KVAdapter interface
• Prefix keys to avoid collisions within a shared KV namespace
• Use Cloudflare KV’s pagination API to implement keys() and clear()
• Wire the package into the monorepo build and test setup

Testing

Automated tests

• Extended the existing KV adapter integration suite in test/kv/int.spec.ts to run against cloudflareKVAdapter alongside the in-memory and Redis adapters, exercising:
  • set, get, has, keys, delete and clear
  • serialisation/deserialisation of values via Cloudflare KV
• Spin up a Miniflare instance in beforeAll with a PAYLOAD_KV namespace and pass its binding into the adapter to mirror how Workers/Pages bindings are provided in production.
• Added a dedicated Cloudflare KV Pagination test when:
  • there are fewer than 1000, exactly 1000, and more than 1000 keys (1000 is the limit)
  • list_complete is true and cursor is omitted by Cloudflare
  • multiple key prefixes share the same KV namespace (ensuring the adapter only returns / clears its own keys)

Manual integration test

1. Created this repo: https://github.com/connorads/payload-cloudflare-kv-test
2. Published the plugin to npm: https://www.npmjs.com/package/@connorads/kv-cloudflare
3. Installed it into a sample Payload app and configured it to use a Cloudflare KV binding
4. Verified basic CRUD behaviour via the simple TODO app