Add EXPLAIN and EXPLAIN EXTENDED query analysis tools

[rocknroll17]

This PR was made from #10

Overview

This PR introduces essential query performance analysis capabilities to the MariaDB MCP Server by adding explain_query and explain_query_extended tools.

Features Added

🔍 explain_query Tool

• Executes EXPLAIN statements to analyze SQL query execution plans
• Provides insights into table access methods, index usage, and join strategies
• Returns structured execution plan data for performance optimization

🔍 explain_query_extended Tool

• Executes EXPLAIN EXTENDED for comprehensive query analysis
• Includes additional performance metrics like filtered row percentages
• Enables deep performance analysis for complex optimization scenarios

Why This Matters

Database queries can vary dramatically in performance - a single line change can transform a millisecond query into one that runs indefinitely. In complex, large-scale databases, query optimization tools are not just helpful but essential for:

• Preventing System Overload: Analyze potentially expensive queries before execution
• Optimizing Performance: Transform inefficient queries through subquery restructuring and join optimization
• Resource Management: Understand query resource consumption patterns
• Development Efficiency: Enable developers to write performant queries from the start

Implementation Details

Security & Safety

• ✅ Supports parameterized queries with proper SQL injection protection
• ✅ Respects read-only mode restrictions
• ✅ Comprehensive error handling and logging
• ✅ Input validation for database and query parameters

API Design

# Basic query analysis
async def explain_query(
    sql_query: str, 
    database_name: str, 
    parameters: Optional[List[Any]] = None
) -> List[Dict[str, Any]]

# Extended query analysis  
async def explain_query_extended(
    sql_query: str,
    database_name: str, 
    parameters: Optional[List[Any]] = None
) -> List[Dict[str, Any]]

Integration

🔗 Seamlessly integrates with existing MCP tool ecosystem
🔗 Follows established patterns from execute_sql implementation
🔗 Consistent error handling and logging approach
🔗 Compatible with current FastMCP framework structure

Impact

This enhancement transforms the MariaDB MCP Server from a basic query execution tool into a comprehensive database performance management platform. These tools are fundamental requirements for any serious database administration and development workflow.

Future Enhancements

• Query optimization suggestions based on execution plans
• Performance benchmarking capabilities
• Integration with query caching strategies
• Automated index recommendation system

Note: These tools are considered essential infrastructure for database performance management and represent a critical gap that needed to be filled in the current MCP server implementation.

[rocknroll17]

Please merge this PR with squash merge. Cause I did a rebase and it became commit log kinda messy.
Thank you.