core[minor]: add upsert, streaming_upsert, aupsert, astreaming_upsert methods to the VectorStore abstraction (#23774)

This PR rolls out part of the new proposed interface for vectorstores
(https://github.com/langchain-ai/langchain/pull/23544) to existing store
implementations.

The PR makes the following changes:

1. Adds standard upsert, streaming_upsert, aupsert, astreaming_upsert
methods to the vectorstore.
2. Updates `add_texts` and `aadd_texts` to be non required with a
default implementation that delegates to `upsert` and `aupsert` if those
have been implemented. The original `add_texts` and `aadd_texts` methods
are problematic as they spread object specific information across
document and **kwargs. (e.g., ids are not a part of the document)
3. Adds a default implementation to `add_documents` and `aadd_documents`
that delegates to `upsert` and `aupsert` respectively.
4. Adds standard unit tests to verify that a given vectorstore
implements a correct read/write API.

A downside of this implementation is that it creates `upsert` with a
very similar signature to `add_documents`.
The reason for introducing `upsert` is to:
* Remove any ambiguities about what information is allowed in `kwargs`.
Specifically kwargs should only be used for information common to all
indexed data. (e.g., indexing timeout).
*Allow inheriting from an anticipated generalized interface for indexing
that will allow indexing `BaseMedia` (i.e., allow making a vectorstore
for images/audio etc.)
 
`add_documents` can be deprecated in the future in favor of `upsert` to
make sure that users have a single correct way of indexing content.

---------

Co-authored-by: ccurme <chester.curme@gmail.com>

libs/core/tests/unit_tests/utils/test_aiter.py

@@ -0,0 +1,31 @@
+from typing import AsyncIterator, List
+
+import pytest
+
+from langchain_core.utils.aiter import abatch_iterate
+
+
+@pytest.mark.parametrize(
+    "input_size, input_iterable, expected_output",
+    [
+        (2, [1, 2, 3, 4, 5], [[1, 2], [3, 4], [5]]),
+        (3, [10, 20, 30, 40, 50], [[10, 20, 30], [40, 50]]),
+        (1, [100, 200, 300], [[100], [200], [300]]),
+        (4, [], []),
+    ],
+)
+async def test_abatch_iterate(
+    input_size: int, input_iterable: List[str], expected_output: List[str]
+) -> None:
+    """Test batching function."""
+
+    async def _to_async_iterable(iterable: List[str]) -> AsyncIterator[str]:
+        for item in iterable:
+            yield item
+
+    iterator_ = abatch_iterate(input_size, _to_async_iterable(input_iterable))
+
+    assert isinstance(iterator_, AsyncIterator)
+
+    output = [el async for el in iterator_]
+    assert output == expected_output

libs/core/tests/unit_tests/utils/test_imports.py

@@ -6,6 +6,8 @@ EXPECTED_ALL = [
     "convert_to_secret_str",
     "formatter",
     "get_bolded_text",
+    "abatch_iterate",
+    "batch_iterate",
     "get_color_mapping",
     "get_colored_text",
     "get_pydantic_field_names",