test(core): add test for doc removed during stream directly after edit

write a test that tests this part:

https://github.com/cycraft/magnetar/blob/9d7eb1efb2fb350e9cfa899adf7be8f4ff6ed3fd/packages/core/src/moduleActions/handleStreamPerStore.ts#L112-L118

steps:
1. open stream for a doc
1. edit a doc locally (core goes into 5 sec writeLock)
2. that doc is deleted from the server side during these 5 seconds
3. the doc gets and stays deleted from local module data after the 5 seconds

potential bug without the highlighted lines (hypothesis):
- it will delete the doc locally _during_ the 5 seconds and is then brought back to life _after_ the 5 seconds write lock

Start by reading packages/core/src/moduleActions/handleStreamPerStore.ts at lines 112-118 and locate the existing core stream tests. Reproduce the five-second write-lock sequence: edit locally, remove the document remotely, then verify the document remains absent from local module data after the lock expires.

Written by the indexing model from the issue text.