community[minor]: llamafile embeddings support (#17976)

* **Description:** adds `LlamafileEmbeddings` class implementation for
generating embeddings using
[llamafile](https://github.com/Mozilla-Ocho/llamafile)-based models.
Includes related unit tests and notebook showing example usage.
* **Issue:** N/A
* **Dependencies:** N/A

libs/community/tests/unit_tests/embeddings/test_llamafile.py

@@ -0,0 +1,67 @@
+import json
+
+import numpy as np
+import requests
+from pytest import MonkeyPatch
+
+from langchain_community.embeddings import LlamafileEmbeddings
+
+
+def mock_response() -> requests.Response:
+    contents = json.dumps({"embedding": np.random.randn(512).tolist()})
+    response = requests.Response()
+    response.status_code = 200
+    response._content = str.encode(contents)
+    return response
+
+
+def test_embed_documents(monkeypatch: MonkeyPatch) -> None:
+    """
+    Test basic functionality of the `embed_documents` method
+    """
+    embedder = LlamafileEmbeddings(
+        base_url="http://llamafile-host:8080",
+    )
+
+    def mock_post(url, headers, json, timeout):  # type: ignore[no-untyped-def]
+        assert url == "http://llamafile-host:8080/embedding"
+        assert headers == {
+            "Content-Type": "application/json",
+        }
+        # 'unknown' kwarg should be ignored
+        assert json == {"content": "Test text"}
+        # assert stream is False
+        assert timeout is None
+        return mock_response()
+
+    monkeypatch.setattr(requests, "post", mock_post)
+    out = embedder.embed_documents(["Test text", "Test text"])
+    assert isinstance(out, list)
+    assert len(out) == 2
+    for vec in out:
+        assert len(vec) == 512
+
+
+def test_embed_query(monkeypatch: MonkeyPatch) -> None:
+    """
+    Test basic functionality of the `embed_query` method
+    """
+    embedder = LlamafileEmbeddings(
+        base_url="http://llamafile-host:8080",
+    )
+
+    def mock_post(url, headers, json, timeout):  # type: ignore[no-untyped-def]
+        assert url == "http://llamafile-host:8080/embedding"
+        assert headers == {
+            "Content-Type": "application/json",
+        }
+        # 'unknown' kwarg should be ignored
+        assert json == {"content": "Test text"}
+        # assert stream is False
+        assert timeout is None
+        return mock_response()
+
+    monkeypatch.setattr(requests, "post", mock_post)
+    out = embedder.embed_query("Test text")
+    assert isinstance(out, list)
+    assert len(out) == 512