feat: add CTE (WITH clause) support to SQL executor

[DidelotK]

Summary

Add support for Common Table Expressions (CTEs) in SQL queries, enabling queries like:

WITH filtered_data AS (
    SELECT id, value FROM source_table WHERE value > 75
)
SELECT * FROM filtered_data

Changes

• Parser (parser.py):

  • Added WITH detection in _detect_query_type() (before UNION check)
  • Added routing for WITH in _parse_components()
  • Added _parse_with_query() method that parses CTE definitions using balanced parenthesis counting

• Executor (executor.py):

  • Added WITH case in execute() method
  • Added _execute_with() method that executes CTEs and stores results in temp views
  • Modified table loading to check temp views before session.table() lookup

Features Supported

• Single CTE: WITH cte AS (...) SELECT * FROM cte
• Multiple CTEs: WITH cte1 AS (...), cte2 AS (...) SELECT * FROM cte2
• Chained CTEs (CTE referencing another CTE)
• CTEs with filtering, aggregation, and column selection
• Case-insensitive WITH keyword
• Proper cleanup of temp views after execution

Test Plan

• 11 new unit tests covering all CTE scenarios
• All 73 session tests pass
• Tested: simple CTE, multiple CTEs, CTE chains, filtering, aggregation, case insensitivity, whitespace handling, parser detection

Known Limitations

• Pre-existing sparkless limitations apply (arithmetic in SELECT, complex AND conditions in WHERE)
• These are not regressions from this PR

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