Allows users to pass multiple query vector as part of a single query
plan. This just runs the queries in parallel without any further
optimization. It's mostly a convenience.
Previously, I think this was only handled by the sync Python remote API.
This makes it common across all SDKs.
Closes https://github.com/lancedb/lancedb/issues/1803
```python
>>> import lancedb
>>> import asyncio
>>>
>>> async def main():
... db = await lancedb.connect_async("./demo")
... table = await db.create_table("demo", [{"id": 1, "vector": [1, 2, 3]}, {"id": 2, "vector": [4, 5, 6]}], mode="overwrite")
... return await table.query().nearest_to([[1.0, 2.0, 3.0], [4.0, 5.0, 6.0], [4.0, 5.0, 6.0]]).limit(1).to_pandas()
...
>>> asyncio.run(main())
query_index id vector _distance
0 2 2 [4.0, 5.0, 6.0] 0.0
1 1 2 [4.0, 5.0, 6.0] 0.0
2 0 1 [1.0, 2.0, 3.0] 0.0
```
Sometimes it is acceptable to users to only search indexed data and skip
and new un-indexed data. For example, if un-indexed data will be shortly
indexed and they don't mind the delay. In these cases, we can save a lot
of CPU time in search, and provide better latency. Users can activate
this on queries using `fast_search()`.
It's useful to see the underlying query plan for debugging purposes.
This exposes LanceScanner's `explain_plan` function. Addresses #1288
---------
Co-authored-by: Will Jones <willjones127@gmail.com>