Python: Add header_provider to Streamable HTTP MCP servers (#4849)

* Python: Add header_provider to MCPStreamableHTTPTool (#4808)

Add a header_provider callback parameter to MCPStreamableHTTPTool that
enables injecting dynamic per-request HTTP headers from runtime kwargs
(originating from FunctionInvocationContext.kwargs set in agent middleware).

The implementation uses contextvars and httpx event hooks to ensure headers
are task-local and safe for concurrent tool calls:

- header_provider receives the runtime kwargs dict and returns headers
- call_tool sets a ContextVar before delegating to MCPTool.call_tool
- An httpx request event hook reads from the ContextVar and injects headers

Example usage:
    mcp_tool = MCPStreamableHTTPTool(
        name="web-api",
        url="https://api.example.com/mcp",
        header_provider=lambda kwargs: {
            "X-Auth-Token": kwargs.get("auth_token", ""),
        },
    )

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address review feedback for #4808: Python: [Bug]: Unable to pass AgentContext to MCPStreamableHTTPTool

* Add test for header_provider via FunctionTool.invoke with FunctionInvocationContext

Addresses PR review comment: exercises the full pipeline from
FunctionInvocationContext.kwargs through FunctionTool.invoke to
MCPStreamableHTTPTool.call_tool and header_provider, rather than
testing call_tool in isolation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address review feedback for #4808: review comment fixes

* Fix streamable MCP transport defaults

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix Azure AI test client mocks

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix MCP runtime kwarg regressions

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Stabilize MCP tool runtime kwargs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Use context kwargs in MCP wrappers

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* updated mcp samples

* fix link

---------

Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/samples/02-agents/mcp/mcp_github_pat.py

@@ -4,7 +4,7 @@ import asyncio
 import os
 
 from agent_framework import Agent
-from agent_framework.openai import OpenAIResponsesClient
+from agent_framework.openai import OpenAIChatClient
 from dotenv import load_dotenv
 
 """
@@ -45,7 +45,7 @@ async def github_mcp_example() -> None:
     # 4. Create agent with the GitHub MCP tool using instance method
     # The MCP tool manages the connection to the MCP server and makes its tools available
     # Set approval_mode="never_require" to allow the MCP tool to execute without approval
-    client = OpenAIResponsesClient()
+    client = OpenAIChatClient()
     github_mcp_tool = client.get_mcp_tool(
         name="GitHub",
         url="https://api.githubcopilot.com/mcp/",