OPTIMIZATION #5: Function pointer dispatch to eliminate switch statement

- Created typedef ColumnProcessor for function pointer type
- Added ColumnProcessors namespace with specialized inline processors:
  * ProcessInteger, ProcessSmallInt, ProcessBigInt, ProcessTinyInt, ProcessBit
  * ProcessReal, ProcessDouble
  * ProcessChar, ProcessWChar, ProcessBinary (handle LOBs, NULL, zero-length)
- Added ColumnInfoExt struct to pass metadata efficiently
- Build columnProcessors array once during cache_column_metadata
- Fast path: Direct function call via columnProcessors[col-1] (no switch)
- Slow path: Fallback switch for complex types (DECIMAL, DATETIME, GUID)
- Eliminates switch evaluation from O(rows × columns) to O(columns)
- All processors use direct Python C API from OPT #1 and OPT #2

Author: bewithgaurav