Upsert that changes datetime field can create duplicates across different indexes

[bountx]

As in the title - upsert action can potentially create duplicates:

1. POST /collections/{id}/bulk_items with body: { "method": "upsert", "items": {...} }

2. When exist_ok=True (UPSERT):

• No duplicate check is performed
• Target index is determined by the new datetime
• If item already exists in old index (with different datetime), it stays there
• Item now exists in TWO indexes

Similair situation happens for PUT /items/{id} (update_item)

Proposed solutions

A) Validate conflict and throw an error 409 if item points at a different index then it would after update
B) Create smart upsert/put that checks indexes for unique key (item_id, collection_id) and if present does DELETE on the duplicate and inserts the new one in the right index

A is short and safe but breaks how upsert works (upsert that should normally call update would now throw an error - but we dont create a duplicate)

B is complicated and risky - instead of standard insert/update we would now have to call DELETE in the process risking deletion on an upsert call