Implement streamable HTTP transport with Redis-based session management

- Add new /mcp endpoint supporting GET, POST, DELETE methods
- Implement SessionManager for Redis-based session state management
- Add MessageDelivery for message buffering when SSE disconnected
- Support horizontal scaling via Redis session storage
- Maintain backwards compatibility with existing /sse and /message endpoints
- Add comprehensive tests for SessionManager functionality
- Session TTL of 5 minutes prevents Redis bloat
- Message buffering for resilient connection handling

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Co-Authored-By: Claude <noreply@anthropic.com>

Author: jerome3o-anthropic