Dune Analytics MCP Server

# Change: Add Query Execution Tools ## Why Query execution is the primary use case for Dune Analytics integration. Agents need both blocking (synchronous) and non-blocking (asynchronous) execution modes to handle queries of varying complexity and duration. ## What Changes - Add `run_query` tool for blocking execution with result waiting - Add `submit_query` tool for non-blocking execution returning execution_id - Add `get_execution_status` tool for checking job state - Add `get_execution_results` tool for retrieving completed job data - Implement proper error mapping for Dune API errors ## Impact - Affected specs: execution-tools (new capability) - Affected code: server.py (add tool definitions) - Dependencies: Requires core-server capability (proposal 1)