Python: [Bug]: BedrockChatClient sends `toolConfig.toolChoice` without `toolConfig.tools` when agent has no tools

[gourab-aiplanet]

Description

When using BedrockChatClient with an Agent that has no tools configured, the client still sends toolConfig.toolChoice to the Bedrock API. This causes a validation error because AWS Bedrock requires toolConfig.tools to be present whenever toolConfig.toolChoice is specified.

Code Sample

import asyncio
from agent_framework import Agent
from agent_framework_bedrock import BedrockChatClient

async def main():
    client = BedrockChatClient(
        access_key="...",
        secret_key="...",
        region="eu-west-1",
        model="anthropic.claude-sonnet-4-6"
    )

    # Agent with no tools
    agent = Agent(
        client=client,
        name="TestAgent",
        instructions="You are a helpful assistant",
        tools=None,  # No tools
        default_options=None,  # No tool options
    )

    # This fails with ParamValidationError
    result = await agent.run("What is AI?")
    print(result)

asyncio.run(main())

Error Messages / Stack Traces

botocore.exceptions.ParamValidationError: Parameter validation failed:
Missing required parameter in toolConfig: "tools"

Package Versions

agent-framework-bedrock version: 1.0.0b260402

Python Version

Python version: 3.10+

Additional Context

Expected behavior

When no tools are provided to the agent, the BedrockChatClient should NOT include toolConfig in the API request at all. This is similar to how PR #4535 fixed the tool_choice="none" case by omitting toolConfig entirely.

Actual behavior

The client sends a request with toolConfig.toolChoice (likely defaulting to {"auto": {}}) but without toolConfig.tools, causing AWS Bedrock to reject the request.