optimizing batch sizing based on cost

[shikhar1729]

Optimize EvaDB

Changes Overview:

• evadb/executor/storage_executor.py : Adjusted the execution of reading data for TableType.NATIVE_DATA by incorporating the specified batch memory size. This ensures efficient resource utilization during data retrieval.

• evadb/optimizer/cost_model.py : Implemented a zero_cost property within the CostModel class, providing a baseline cost entry for comparison. Revised the calculate_cost method to accept a list of children costs, enabling a more accurate representation of overall costs. Enhanced the cost calculation for various plan types, taking into account child costs and adjusting accordingly.

• evadb/optimizer/group_expression.py : Improved the representation of GroupExpression instances for better clarity and debugging.

• evadb/optimizer/optimizer_tasks.py : Modified the execution logic within the OptimizeInputs task to consider child costs when calculating the overall cost. This adjustment ensures a more accurate representation of the optimization process.

• evadb/optimizer/rules/rules.py : Refined the application of rules related to LogicalGet instances, specifically addressing batch memory size configuration within the SeqScanPlan. Experimentation with heuristics for optimal batch memory size is also noted for future consideration.

• evadb/plan_nodes/vector_index_scan_plan.py : Improved the __str__ method for better readability and understanding of VectorIndexScan instances.