community[minor]: Prem AI langchain integration (#19113)

### Prem SDK integration in LangChain

This PR adds the integration with [PremAI's](https://www.premai.io/)
prem-sdk with langchain. User can now access to deployed models
(llms/embeddings) and use it with langchain's ecosystem. This PR adds
the following:

### This PR adds the following:

- [x]  Add chat support
- [X]  Adding embedding support
- [X]  writing integration tests
    - [X]  writing tests for chat 
    - [X]  writing tests for embedding
- [X]  writing unit tests
    - [X]  writing tests for chat 
    - [X]  writing tests for embedding
- [X]  Adding documentation
    - [X]  writing documentation for chat
    - [X]  writing documentation for embedding
- [X] run `make test`
- [X] run `make lint`, `make lint_diff` 
- [X]  Final checks (spell check, lint, format and overall testing)

---------

Co-authored-by: Anindyadeep Sannigrahi <anindyadeepsannigrahi@Anindyadeeps-MacBook-Pro.local>
Co-authored-by: Bagatur <baskaryan@gmail.com>
Co-authored-by: Erick Friis <erick@langchain.dev>
Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>

libs/community/tests/integration_tests/chat_models/test_premai.py

@@ -0,0 +1,70 @@
+"""Test ChatPremAI from PremAI API wrapper.
+
+Note: This test must be run with the PREMAI_API_KEY environment variable set to a valid 
+API key and a valid project_id. 
+For this we need to have a project setup in PremAI's platform: https://app.premai.io
+"""
+
+import pytest
+from langchain_core.messages import BaseMessage, HumanMessage, SystemMessage
+from langchain_core.outputs import ChatGeneration, LLMResult
+
+from langchain_community.chat_models import ChatPremAI
+
+
+@pytest.fixture
+def chat() -> ChatPremAI:
+    return ChatPremAI(project_id=8)
+
+
+def test_chat_premai() -> None:
+    """Test ChatPremAI wrapper."""
+    chat = ChatPremAI(project_id=8)
+    message = HumanMessage(content="Hello")
+    response = chat([message])
+    assert isinstance(response, BaseMessage)
+    assert isinstance(response.content, str)
+
+
+def test_chat_prem_system_message() -> None:
+    """Test ChatPremAI wrapper for system message"""
+    chat = ChatPremAI(project_id=8)
+    system_message = SystemMessage(content="You are to chat with the user.")
+    human_message = HumanMessage(content="Hello")
+    response = chat([system_message, human_message])
+    assert isinstance(response, BaseMessage)
+    assert isinstance(response.content, str)
+
+
+def test_chat_prem_model() -> None:
+    """Test ChatPremAI wrapper handles model_name."""
+    chat = ChatPremAI(model="foo", project_id=8)
+    assert chat.model == "foo"
+
+
+def test_chat_prem_generate() -> None:
+    """Test ChatPremAI wrapper with generate."""
+    chat = ChatPremAI(project_id=8)
+    message = HumanMessage(content="Hello")
+    response = chat.generate([[message], [message]])
+    assert isinstance(response, LLMResult)
+    assert len(response.generations) == 2
+    for generations in response.generations:
+        for generation in generations:
+            assert isinstance(generation, ChatGeneration)
+            assert isinstance(generation.text, str)
+            assert generation.text == generation.message.content
+
+
+async def test_prem_invoke(chat: ChatPremAI) -> None:
+    """Tests chat completion with invoke"""
+    result = chat.invoke("How is the weather in New York today?")
+    assert isinstance(result.content, str)
+
+
+def test_prem_streaming() -> None:
+    """Test streaming tokens from Prem."""
+    chat = ChatPremAI(project_id=8, streaming=True)
+
+    for token in chat.stream("I'm Pickle Rick"):
+        assert isinstance(token.content, str)