[feature][agent][mcp][bounty-eligible] Support multi-MCP execution and direct model initialization

[ascender1729]

Description:
This PR enhances Swarms agents by enabling connectivity to multiple MCP (Modular Command Protocol) servers simultaneously, allowing tools to be executed across different microservices. The implementation supports both configuring MCP URLs directly through the agent constructor and via environment variables.

Key Features:

• Support for multiple MCP servers through mcp_urls parameter or MCP_URLS environment variable
• New handle_multiple_mcp_tools method for executing tools across different servers
• Added execute_mcp_call function for direct server-specific tool execution
• Enhanced error handling with retry logic for reliable tool execution
• Robust JSON payload extraction from model responses
• Complete documentation of the multi-MCP workflow and payload format
• Example servers (weather_server.py and news_server.py) for testing

Impact:

• Enables distributed tool execution across specialized microservices
• Improves system architecture by separating tool concerns
• Provides fault tolerance through connection to multiple servers
• Maintains backward compatibility with existing single-server implementations

Issue:
Closes #881

Testing:

• Added unit tests in test_multi_mcp.py
• Created end-to-end examples with local MCP servers
• Manual verification with demo servers

Tag maintainer:
@kyegomez

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📚 Documentation preview 📚: https://swarms--891.org.readthedocs.build/en/891/