Deleting the cache entry inside the upload.complete event makes the completing request itself return 410

**Version:** v2.4.0

## Summary

If a host application deletes the upload's cache entry from inside the `tus-server.upload.complete` event handler (a natural pattern for "consume the upload on completion" flows), the server's own post-event re-read of that entry causes the very request that just succeeded to respond **410 Gone** — the client is told its successful upload failed, and clients like Uppy surface an error for an upload that actually completed.

## Reproduce

1. Register a listener on `tus-server.upload.complete` that processes the finished file and then deletes the upload's cache entry (e.g. `$cache->delete($key)`).
2. Complete an upload (final PATCH).
3. The PATCH response is 410 instead of 204, despite the file having been fully received and the listener having run successfully.

## Workaround we use

Defer cache retirement until after the response object is built, within the same request.

## Suggested fix

Snapshot the file/cache state needed for the response before dispatching the completion event, or document that the cache entry must outlive the event handler.