[Feature] KV BulkGet API Endpoint

### Is there an existing issue for this? - [x] I have searched the existing issues ### Description The Worker-RS implementation appears to be missing the bulkGet endpoint described here: https://developers.cloudflare.com/api/node/resources/kv/subresources/namespaces/methods/bulk_get/ I can see that struct shows get, but not bulkGet. https://docs.rs/worker/latest/worker/kv/struct.KvStore.html --- Edit: **Whoops**. I blankly assumed that workers-rs was calling API, but the Rest API != the runtime api. That said, the js runtime api does support bulk gets too. I've created a PR to implement it, and tested it with Miniflare to confirm it works.