add anthropic native support

[victordibia]

Claude 3.7 just came out. Its a pretty capable model and it would be great to support it in Autogen.
This will could augment the already excellent support we have for Anthropic via the SKAdapters in the following ways

• Based on the ChatCompletion API similar to the ollama and openai client
• Configurable/serializable (can be dumped) .. this means it can be used easily in AGS.

What is Supported

(video below shows the client being used in autogen studio)
https://github.com/user-attachments/assets/8fb7c17c-9f9c-4525-aa9c-f256aad0f40b

• streaming
• tool callign / function calling
• drop in integration with assistant agent.
• multimodal support

from dotenv import load_dotenv
import os 

load_dotenv()

from autogen_agentchat.agents import AssistantAgent
from autogen_agentchat.ui import Console
from autogen_ext.models.openai import OpenAIChatCompletionClient
from autogen_ext.models.anthropic import AnthropicChatCompletionClient 
model_client =   AnthropicChatCompletionClient(
        model="claude-3-7-sonnet-20250219" 
    )

async def get_weather(city: str) -> str:
    """Get the weather for a given city."""
    return f"The weather in {city} is 73 degrees and Sunny."

 
agent = AssistantAgent(
    name="weather_agent",
    model_client=model_client,
    tools=[get_weather],
    system_message="You are a helpful assistant.", 
    # model_client_stream=True,   
)

# Run the agent and stream the messages to the console.
async def main() -> None:
    await Console(agent.run_stream(task="What is the weather in New York?"))
await main()

result

messages = [
    UserMessage(content="Write a very short story about a dragon.", source="user"),
]

# Create a stream.
stream = model_client.create_stream(messages=messages)

# Iterate over the stream and print the responses.
print("Streamed responses:")
async for response in stream:  # type: ignore
    if isinstance(response, str):
        # A partial response is a string.
        print(response, flush=True, end="")
    else:
        # The last response is a CreateResult object with the complete message.
        print("\n\n------------\n")
        print("The complete response:", flush=True)
        print(response.content, flush=True)
        print("\n\n------------\n")
        print("The token usage was:", flush=True)
        print(response.usage, flush=True)

Why are these changes needed?

Related issue number

Closes #5205
Closes #5708

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

cc @rohanthacker

[codecov]

Codecov Report

Attention: Patch coverage is 24.03259% with 373 lines in your changes missing coverage. Please review.

Project coverage is 73.47%. Comparing base (1f30622) to head (70e2250).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
.../autogen_ext/models/anthropic/_anthropic_client.py	14.45%	361 Missing ⚠️
...xt/src/autogen_ext/models/anthropic/_model_info.py	33.33%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5695      +/-   ##
==========================================
- Coverage   75.75%   73.47%   -2.29%     
==========================================
  Files         171      175       +4     
  Lines       10637    11128     +491     
==========================================
+ Hits         8058     8176     +118     
- Misses       2579     2952     +373     

Flag	Coverage Δ
unittests	73.47% <24.03%> (-2.29%)	⬇️

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