fix(mistralai): handle HTTP errors in async embed documents (#33187)

The async embed function does not properly handle HTTP errors.

For instance with large batches, Mistral AI returns `Too many inputs in
request, split into more batches.` in a 400 error.

This leads to a KeyError in `response.json()["data"]` l.288

This PR fixes the issue by:
- calling `response.raise_for_status()` before returning
- adding a retry similarly to what is done in the synchronous
counterpart `embed_documents`

I also added an integration test, but willing to move it to unit tests
if more relevant.

libs/partners/mistralai/tests/integration_tests/test_embeddings.py

@@ -1,5 +1,11 @@
 """Test MistralAI Embedding."""
 
+from unittest.mock import patch
+
+import httpx
+import pytest
+import tenacity
+
 from langchain_mistralai import MistralAIEmbeddings
 
 
@@ -29,6 +35,21 @@ async def test_mistralai_embedding_documents_async() -> None:
     assert len(output[0]) == 1024
 
 
+async def test_mistralai_embedding_documents_http_error_async() -> None:
+    """Test MistralAI embeddings for documents."""
+    documents = ["foo bar", "test document"]
+    embedding = MistralAIEmbeddings(max_retries=0)
+    mock_response = httpx.Response(
+        status_code=400,
+        request=httpx.Request("POST", url=embedding.async_client.base_url),
+    )
+    with (
+        patch.object(embedding.async_client, "post", return_value=mock_response),
+        pytest.raises(tenacity.RetryError),
+    ):
+        await embedding.aembed_documents(documents)
+
+
 async def test_mistralai_embedding_query_async() -> None:
     """Test MistralAI embeddings for query."""
     document = "foo bar"