[Feature Request]: Set ef_search per query

### Describe the problem

Currently we only set the `ef_search` parameter when we init the index, usually on creation of a `Collection`. However, this parameter is actually per-query at the level of HNSW.

Generally we only need to set this parameter once since in principle there is a 'best' setting for the average case on any collection, but there are cases where we may want to let the user set it dynamically, for example to conduct a parameter sweep against a particular dataset.

Additionally, EF should be at least as large as the number of elements we want to return, which means it may have to be dynamic anyway.

### Describe the proposed solution

Allow EF search to be set on a per-query basis.

### Alternatives considered

_No response_

### Importance

would make my life easier

### Additional Information

This is somewhat of a pain in the ass. Besides piping in this parameter on query (which now creates the need for a `query_parameters` argument...) the way the HNSW implementation handles this is, also, bad, since it's set as a property of the index: https://github.com/chroma-core/hnswlib/blob/d52dd85106c5a1955a7dbd745a76ba2a8259451a/hnswlib/hnswalg.h#L33

even though it's only a property of each *query*.

To do this 'right' (for example, to handle concurrency correctly), it would take a refactor of our HNSW impl too.

Start by tracing how Collection initialization currently sets ef_search and how query requests reach the HNSW implementation. Read hnswlib's hnswalg.h at the linked location, then determine the changes needed for a per-query parameter and concurrency-safe handling; done means callers can set ef_search dynamically, including values based on requested result counts.

Written by the indexing model from the issue text.